Ditto everyone else -- walk away.
Walk away not only for the all the reasons already stated but, worse than that, there's the emotional attachment your daughter will form with the horse.
That attachment is going to start the moment you say "yes", regardless of whether you are tucking her into jammieland or fixing her breakfast before she heads out the door for school, where she will tell all her friends about her new horse.
A horse that sounds as if, physically
, is not going to able to perform the intended job.
I have three horses who can no longer perform their original jobs and only have a "slight lameness". They were trail horses; die hard, dig up the hill and slide back down it, hard working trail horses. That "slight lameness" is masking some very serious issues because I spend so much time and effort trying to keep them comfortable. They aren't drugged in the sense you speak of but they are on anti-inflammatories, come in at night and get poulticed and wrapped when that "slight lameness" elevates.
They've been with me 11, 19, & 6 years, so will remain until their Times come but, it isn't cheap and there's a lot of work to keep two of them comfortable.
That is NOT something you want to get involved in when buying a first horse for your daughter.
Your Mother's Intuition is already sending off signals, elst you wouldn't be asking for input in here. Listen to it
I hope we have all helped