The horse is young and, while I don't have a problem lightly starting a 2 year old if they seem to be ready, she doesn't sound ready at all.
There is a lot more to training a horse than just putting a saddle up there and getting on. Before you ever set foot in a stirrup, the horse needs to know how to bend and give to the bit every which way. They need to have a solid whoa and a solid cue for forward motion.
Did gf do any kind of warm up with the horse in a roundpen or anything or did she just put the saddle on and proceed to get on?
Either way, that horse needs to be given time to mature, another year at least, and then needs to go to a trainer that will know how to get her started right.
No offense, but if your gf keeps going the way she's been going, she's either going to get herself hurt, get the horse hurt, or completely fry the poor filly's brain and she may never be a trustworthy mount.