The SBU track is a very old track in poor condition, still 440 yards. There is a track about 4-5 minutes from the sports complex (about 2 min from the train station) at the Stony Brook Prep School that is in good shape and 400 meters. Not sure if people that don't go there are allowed to use it or not but I've never been kicked off.
There are some trails near the Avalon Park at the bottom of 25A (between 1.5-2mi from campus depending on which way you take to get there, 25A or Cedar --> Christian --> Sand) that are pretty decent, I run on those pretty often. If you go out the South P exit and take a right at the light (almost exactly 2 miles from the Sports Complex if you start at the entrance across from the stadium), right at the top of the hill less than a quarter mile is the entrance to Gyrodine Park/Flowerfield (has some other names), the gate is closed on Sundays but usually open other days, and sometimes you can still slip through if you are small enough. Our XC course was in there this past year, there is construction being done now, but towards the end of the summer it wasn't so bad that we couldn't get runs done in there still.
There are also a few in the power lines but if you don't know where you're going you could get lost pretty easily, when you come out you have to go through a couple residential roads, through someone's backyard and under part of the hospital to get back on campus. Otherwise most of our runs are on the roads. A loop around campus is roughly 3 miles if she wants to do some short runs.