I missed some of what you posted before the delete - but I asked before if you’ve done a extensive blood panel on this horse since he’s been in the states. Have you? Sometimes what we spend thousands of dollars on blocking, xrays, ultrasounds, etc… actually turns out to be something more systemic.
I do hope you have taken some of this advice to heart and try to get this young horse some real time off - even if it means moving to a rehab farm for a bit for the turnout that it sounds like he needs.
And - please, please see if you can get your daughter some lessons/lease on a schoolmaster. Forgive me - but the few vids I watched of her riding - she’s a lovely young rider and will be a very nice rider with some miles on her, but she’s green and the horse is young. They will benefit in the long run if she’s got some more tools available to her that usually only comes from miles and lessons on a horse that has been there, done that.
What’s the saying? “green on green usually equals black and blue”. I am by no means saying she is a bad rider, but she is not at the level that will have her seeing the Olympics in 4 or 8 years. I love to see enthusiasm from young riders, but it is easy to get discouraged without more realistic goals for her in the next couple years to aim for.
Start by getting the horse as sound as possible. Whether that is 2 months or 12 months, if she’s constantly chasing a lameness issue, she’s going to get frustrated very quickly.
I know $70k is a large amount of money, but it’s a pittance compared to what you will have to spend to even get her NAYC competitive. I have no idea what your finances look like, but with a teen you need to be prepared to determine just how much money you’re willing to spend. I can think of at least 5 teen riders from my area whose parents went into substantial debt only to have the teen give up riding by the time they reach 18, And every single one of them imagined they’d be on the senior US team by the time they finished high school.