She doesn't look too big to me. Perhaps she's not what the judges are used to size-wise (i.e. Tiny kids on ponies, & everyone else on large horses), but she certainly isn't big enough to be causing the pony any problems. I can see where her long torso may give the illusion that she might be a bit mis-proportioned to the pony, but when you look at her leg, it appears to me that even when stretched all the way down, it'd still be hitting her pony at an appropriate spot. "Too big", to me, means that either a) you physically weigh too much for your pony, or b) your legs are too long to properly give aids, neither of which appears to be the case here at the moment.