I don’t necessarily think boarding school is a bad idea for this OP either, but I think this boarding school might be.
@LilahEquestrian, I went to a very well-known all girls boarding school with a stand out equestrian program in the very early 00’s. Tuition even then was over $48K/year and board was $1150 before lessons (we had to take a minimum of 2 per week). I was showing heavily on the AA circuit before going there and continued to show heavily after leaving and I can honestly say that the school did not make or break the riding careers of ANYONE I know. I do know that a few girls have since gone back and worked for my school as professionals, but their junior and amateur careers were far more extensive than showing school-owned horses. One had a whole string of hunters, jumpers, and Big Eq horses and the other was an incredibly successful Big Eq rider with a super nice high junior jumper. We had some lovely school horses, but those weren’t the horses that defined anyone’s junior career.
I am going to say this as someone who was lucky enough to have the funds and the familial support to go to boarding school and continue my riding career; it is simply not going to do for you what you think it will. At least not in terms of reaching your goal of being a professional rider. Now, if we’re talking academically, that may be an entirely different story, particularly given your current educational situation. But that said, you’d be FAR better off leasing/selling your horse and diving headlong into your academics and making that the focus of your time there. If you can ride and be on their varsity team and have some showing opportunities, that’s great! But having one 3’3" junior hunter is not going to get you on an NCAA team. But doing extremely well academically, applying to strong colleges, and choosing a major with a lucrative career path will afford you to do so much more in this sport than your current plan. Being a professional isn’t all its cracked up to be and for every BNT there are hundreds upon hundreds of struggling pros who can barely make ends meet each month.
If horses were out of the equation, what other things might you be interested in doing? Based on your answer to that question, then explore what possible career paths will most likely result in a solid financial future that will allow you to have the riding career you want. In that vein, is it too late to apply to other boarding/day schools with lower tuition and better academics? I feel like this would be your smartest move.
Best of luck!!