These are good descriptions, but I would take the "easy" trails as targeted for families and children. I am sure your wife can handle any of the moderate hikes. I did the Bear Lake to Emerald Lake while recovering after recovering from a serious injury, so I was not in running shape and it was not in the least bit challenging. I did Flatop as a 12 year old kid and aside from altitude sickness it was not a problem.
Easy
Bear Lake Trail. The virtually flat nature trail around Bear Lake is an easy, 1-mi walk that's wheelchair and stroller accessible. Sharing the route with you will likely be plenty of other hikers as well as songbirds and chipmunks. Easy. Trailhead at Bear Lake, Bear Lake Rd., Rocky Mountain National Park, CO, 80517.
Copeland Falls. The 0.6-mi hike to these Wild Basin Area falls is a good option for families, as the terrain is relatively flat (there's only a 15-foot elevation gain). Easy. Trailhead at Wild Basin Ranger Station, Rocky Mountain National Park, CO, 80517.
Cub Lake. This 4.6-mi, three-hour (round-trip) hike takes you through meadows and stands of aspen trees and up 540 feet in elevation to a lake with water lilies. Easy. Trailhead at Cub Lake, 1.7 mi from Moraine Park Campground, Rocky Mountain National Park, CO, 80517.
East Inlet Trail. An easy hike of 0.3 mi from East Inlet trailhead, just outside the park in Grand Lake, will get you to Adams Falls in about 15 minutes. The area around the falls is often packed with visitors, so if you have time, continue east to enjoy more solitude, see wildlife, and catch views of Mount Craig from near the East Meadow campground. Note, however, that the trail beyond the falls has an elevation gain of between 1,500 and 1,900 feet, making it a more challenging hike. Easy. Trailhead at East Inlet, end of W. Portal Road (CO 278) in Grand Lake, Grand Lake, CO, 80447.
Glacier Gorge Trail. The 4.5-mi hike to Mills Lake can be crowded, but the reward is one the park's prettiest lakes, set against the breathtaking backdrop of Longs Peak, Pagoda Mountain, and the Keyboard of the Winds. There's a modest elevation gain of 700 feet. On the way, about 1 mi in, you pass Alberta Falls, a popular destination in and of itself. The hike travels along Glacier Creek, under the shade of a subalpine forest. Give yourself at least four hours for hiking and lingering. Easy. Trailhead off Bear Lake Rd., about 1 mi southeast of Bear Lake, Rocky Mountain National Park, CO, 80517.
Sprague Lake. With virtually no elevation gain, this 1-mi, pine-lined path near a popular backcountry campground is wheelchair accessible and provides views of Hallet Peak and Flattop Mountain. Easy. Trailhead at Sprague Lake, Bear Lake Rd., 4.4 mi southwest of Moraine Park Visitor Center, Rocky Mountain National Park, CO, 80517.
Moderate
Bear Lake to Emerald Lake. This scenic, caloric-burning hike begins with a moderately level, ½ mi journey to Nymph Lake. From here, the trail gets steeper, with a 425-foot elevation gain, as it winds around for 0.6 mi to Dream Lake. The last stretch is the most arduous part of the hike, an almost all-uphill 0.7-mi trek to lovely Emerald Lake, where you can perch on a boulder and enjoy the view. All told, the hike is 3.6 mi, with an elevation gain of 605 feet. Allow two hours or more, depending on stops. Moderate. Trailhead at Bear Lake, off Bear Lake Rd., 7.9 mi southwest of the Moraine Park Visitor Center, Rocky Mountain National Park, CO, 80517.
Colorado River Trail. This walk to the ghost town of Lulu City on the west side of the park is excellent for looking for the bighorn sheep, elk, and moose that reside in the area. Part of the former stagecoach route that went from Granby to Walden, the 3.1-mi trail parallels the infant Colorado River to the meadow where Lulu City once stood. The elevation gain is 300 feet. Moderate. Trailhead at Colorado River, off Trail Ridge Rd., 1.7 mi north of the Timber Creek Campground, Rocky Mountain National Park, CO, 80517.
Fern Lake Trail. Heading to Odessa Lake from the north involves a steep hike, but on most days you'll encounter fewer other hikers than if you had begun the trip at Bear Lake. Along the way, you'll come to the Arch Rocks; the Pool, an eroded formation in the Big Thompson River; two waterfalls; and Fern Lake (4.9 mi from your starting point). Odessa Lake itself lies at the foot of Tourmaline Gorge, below the craggy summits of Gabletop Mountain, Little Matterhorn, Knobtop Mountain, and Notchtop Mountain. For a full day of spectacular scenery, continue past Odessa to Bear Lake (9 mi total), where you can pick up the shuttle back to the Fern Lake Trailhead. Moderate. Trailhead off Bear Lake Rd., about 2.5 mi south of Moraine Park Visitor Center, Rocky Mountain National Park, CO, 80517.
Mills Lake. From this popular spot, you can admire the Keyboard of the Winds, a jagged ridge connecting Pagoda and Longs Peaks that looks like the top of a spiny reptile's back. The 5.6-mi hike gains 750 feet in elevation as it takes you past Alberta Falls and Glacier Falls en route to the shimmering lake at the mouth of Glacier Gorge. Moderate. Trailhead at Glacier Gorge Junction, 1.1 mi from Bear Lake, Rocky Mountain National Park, CO, 80517.
Continental Divide National Scenic Trail. This 3,100-mi corridor, which extends from Montana's Canadian border to the southern edge of New Mexico, enters Rocky Mountain National Park in two places, at trailheads only about 4 mi apart and located on either side of the Kawuneeche Visitor Center on Trail Ridge Road, at the park's southwestern end. Within the park, it covers about 30 mi of spectacular montane and subalpine terrain and follows the existing Green Mountain, Tonahutu Creek, North Inlet, and East Shore Trails. Moderate. Trailheads at Harbison Meadows Picnic Area, off Trail Ridge Rd., about 1 mi inside park from Grand Lake Entrance, and at East Shore Trailhead, just south of Grand Lake, Rocky Mountain National Park, CO, 80517.
Difficult
Bluebird Lake Trail. The 6-mi climb from the Wild Basin trailhead to Bluebird Lake (2,478-feet elevation gain) is especially scenic. You pass Copeland Falls, Calypso Cascades, and Ouzel Falls, plus an area that was burned in a lightning-instigated fire in 1978—today a mix of bright pink fireweed and charred tree trunks. Difficult. Trailhead at Wild Basin Ranger Station, about 2 mi west of Wild Basin Entrance Station off Rte. 7, 12.7 mi south of Estes Park, Rocky Mountain National Park, CO, 80517.
Chapin Pass. This is a tough hike, but it comes with great views of the park's eastern lower valleys. It's about 3½ mi one-way, including a 2,874-foot gain in elevation to the summit of Ypsilon Mountain (elevation 13,514 feet); you pass the summits of Mount Chapin and Mount Chiquita on the way. From the trailhead, the path heads downhill to Chapin Creek. For a short distance after leaving the trailhead, keep a sharp eye out to the right for a less obvious trail that heads uphill to the treeline and disappears. From here head up along the steep ridge to the summit of Mount Chapin. Chiquita and Ypsilon are to the left, and the distance between each peak is about 1 mi and involves a descent of about 400 feet to the saddle and an ascent of 1,000 feet along the ridge to Chiquita. From Ypsilon's summit you'll look down 2,000 feet at Spectacle Lakes. You may wish to bring a topo map and compass. Difficult. Trailhead at Chapin Pass, off Old Fall River Rd., about 6.5 mi from the Endovalley Picnic Area, Rocky Mountain National Park, CO, 80517.
Chasm Lake Trail. Nestled in the shadow of Longs Peak and Mount Meeker, Chasm Lake offers one of Colorado's most impressive backdrops, which also means you can expect to encounter plenty of other hikers on the way. The 4.2-mi Chasm Lake Trail, reached via the Longs Peak Trail, has a 2,360-foot elevation gain. Just before the lake, you'll need to climb a small rock ledge, which can be a bit of a challenge for the less surefooted; follow the cairns for the most straightforward route. Once atop the ledge, you'll catch your first memorable view of the lake. Difficult. Trailhead at Longs Peak Ranger Station, off Rte. 7, 10 mi from the Beaver Meadows Visitor Center, Rocky Mountain National Park, CO, 80517.
Deer Mountain Trail. This 6-mi round-trip trek to the top of 10,083-foot Deer Mountain is a great way for hikers who don't mind a bit of a climb to enjoy the views from the summit of a more manageable peak. You'll gain more than 1,000 feet in elevation as you follow the switchbacking trail through ponderosa pine, aspen, and fir trees. The reward at the top is a panoramic view of the park's eastern mountains. Difficult. Trailhead at Deer Ridge Junction, 4.1 mi west of Moraine Park Visitor Center, U.S. 34 at U.S. 36, Rocky Mountain National Park, CO, 80517.
Longs Peak Trail. Climbing this 14,259-foot mountain (one of 54 "Fourteeners" in Colorado) is an ambitious goal for almost anyone—but only those who are very fit and acclimated to the altitude should attempt it. The 16-mi round-trip climb requires a predawn start (3 am is ideal), so that you're off the summit before the typical summer afternoon thunderstorm hits. Also, the last 2 mi or so of the trail are very exposed—you have to traverse narrow ledges with vertigo-inducing drop-offs. That said, summiting Longs can be one of the most rewarding experiences you'll ever have. The Keyhole route is the most popular means of ascent, and the number of people going up it on a summer day can be astounding, given the rigors of the climb. Though just as scenic, the Loft route, between Longs and Mount Meeker from Chasm Lake, is less crowded but not as clearly marked and therefore more difficult to navigate. Difficult. Trailhead at Longs Peak Ranger Station, off Rte. 7, 10 mi from Beaver Meadows Visitor Center, Rocky Mountain National Park, CO, 80517.