I have to say I agree with JustDressageIt. You can't really tell how a horse is going to jump when they're so young. She looks great now, yeah, but that could change in a few years.
And, I don't know much about foals since I never raised one, but I don't think her legs are going to get much longer anyway. They will get more muscle, maybe slightly longer/taller, but not in comparison to the rest of her body. She has so little to lift now. Though I know you didn't make your horse jump this high, check out this video:
With their long legs and tiny bodies, I can imagine most foals are great jumpers.