The one part you and I might differ on is on her ability to improve dramatically. At 10M and less I'm on board. It would be a shock to see her make any dramatic strides there. A few seconds a mile over her first few seasons or something would be very good. The marathon she should, and will, make dramatic improvements in. It's the one race that requires more than just a great aerobic base, and it's wayyy worse than her other races. I don't think you can go and give her 2:27...but bringing proper focus and mileage I expect her to do like almost every other runner that focuses on marathoning does, and bring her marathon into the normal range of what you'd expect a 71' half runner to do; so somewhere between 2:28 and 2:33 or so depending on just how her fatigue resistance, economy, etc. are.
If you don't expect her in current fitness, with marathon training, to have a shot at being near 2:30 I think you're hugely underselling her.
Where it's interesting with her is that she starts from a level of aerobic fitness that is essentially "Trials Longshot". Her fitness will probably* get a little better, with the slight chance she gets significantly better and the slight chance she gets slightly worse (*I've seen a few people, though rare, who seem to do better with a mix).
The thing that makes it interesting is that she is already at 71' or so. That's pretty good. If she found 10/s a mile in running improvement we'd be talking 68 or so for half. A 10/s mile improvement would be a big chunk but it's not an unreasonable or unheard of thing for a runner to take 30s off a 5k PR over the course of several seasons, even for seasoned runners.
68 for the half is Jordan/Shalane territory. Whether she can do it comes down to two things:
1) Does she take fairly well to the marathon? This is a total unknown, and I don't think we have any way to make a good guess
2) Does she have 10/s or so per mile to make in aerobic/running fitness gains over 5 or 6 seasons? It's a big improvement, but not so much as to be implausible.
Where does that leave us odds wise? To me a worse case scenario would be able a 10%-20% chance of #1. A decent number of runners are acceptable marathoners. The chances of her being a Hasay level marathon talent are, of course, quite low. Well below 1% I think. For part 2, that's hard to speculate on, but I'd say that's probably on the order of 10% to maybe as high as 40% depending on how much you think she will benefit from switching to full time running.
Those estimates give between a 1% and 8% chance of reaching a level compared to Shalane/Hasay level. Not great odds, but enough to make it interesting and not a pie in the sky wild goose chase.
Olympic Gold on the other hand....well she needs #1, but then probably needs to improve by 15-20s mile. That I'd have to guess the odds are well below 1% she can improve that much.