YTA, as someone who went through almost the exact situation, I'm still recovering after 10 years.
Special needs kids need their parents even more than regular kids. I grew massive abandonment issues because my parents weren't around much in the earlier stages of my life.
Don't tell your daughter anything that makes her feel dumb or not good enough. My grades went up 20-30% after my mom stopped telling me to "perform at a level appropriate to your age"
Is that school really legit? A boarding school for challenged kids sounds like a recipe for disaster unless the ratios are like, 1:3 for staff to students at most, and even then shitshows happen all the time even at the top institutions here. My cousin went to one of these specialized boarding schools and it cost him nearly 100k a year, and even then the accommodations could only be described as mediocre.
FOUR other kids? Nooooooooooo. Most kids with learning disabilities can't deal with noise. Four kids is bound to be noisy.
My parents' marriage is fine after my mom stayed to take care of me, but I'm lucky they both prioritized me above a more comfortable romantic life.
Business operations, and head of operations. Based on this, I'll assume you're a bit more well-off. If you aren't, sorry for the assumption, but if you are, please don't cheap out on a safe environment for your daughter. $2k a month is absolutely worth it because therapy is much more long term and also pretty damn pricey.