Welcome to the world of jumping!!
Horses 3years and up all regularly jump huge from a young age....hence you never see an old grand prix horse! They are all nakered by the age of 16yrs!
Most jump owners/yards feed balancers, joint supplements, and anything else they can think of to aid the horse. Its something they seem to do! X-rays will tell you more.
The problem is she can jump big so all they wana do is jump big...this doesnt mean that she has been jumped big all the time it just means that they wana show that off.
If you want her girl, then make sure you do your homework and get those x-rays, id also recomend a full body bone scan as that will show up any joint/muscle body problems well before they happen!
Shes stunning! Just too keen to a fence and hasnt been told how to jump properly! Jump excercises will get her to wait for the fence to come to her, to make the correct shape and use herself correctly! All of this can be done! She is just your typical 5year old that has been jumped, way too keen! This doesnt make her a problem! Just means she needs to go hacking and get out and about and enjoy herself instead of expecting to jump all the time!