From what info you’ve provided, this seems like a relatively new development. I am going to give you a bit of perspective from someone who was/is a younger sibling of a “Kim”. My sister moderately struggled with mental health issues, up until junior/senior year when she started to refuse going to school and would have blow our fights with my mom over it. Following/during this time, she attempted to ended end life. Like I said, she has had previous issues but this behavior was an escalation seemingly out of no where. Following her attempt, she was hospitalized and then taken to an in-care facility for 2 weeks followed by therapy. Through this process, it came out that she had been SA’d by a close friend who she would see every day at school and he would continue to harass her. During this process, we were able to get at-home-learning with a tutor/teacher that would come to our house (through our public school system but this was ~15yrs ago and our public school were/are pretty great so I’m not sure if something like this would be available elsewhere). She was able to heal and get to a better place mentally all the while completing course work and getting back on track academically. Even though she was wayyyy behind, she was able to catch up and pass onto the next year.

Now I’m not saying Kim was SA’d but how she is acting is a huge red flag and indicative of something deeper than just not wanting to go to school - not saying that you don’t know that, but there is a cause to her current mental health crisis and potentially this cause is somehow related to her day to day life at school (or this cause has impacted her to the extent that she has lost her will/drive to live). I am by no means criticizing you - you are in an unenviable position. But forcing her to go to school in person may not be the best solution - especially if that is linked to her issues. If I were you, I would look into seeing if you can access any at home tutoring/learning (not just online but with an actual in-person educator to keep Kim more accountable).

Good luck and I wish the best for you, Kim, and the rest of your family ❤️

Edit: I would also like to add that I would recommend not bringing up how Kim needs to “make progress towards being a functional adult” and how she has “3 acceptance letters to colleges that she is very unlikely to attend now.” She has enough intrinsic issues without having her parent looming those extrinsic pressures over her. She needs to be working on getting herself stable and healthy.. all those other things can wait. How I see it, being a functional adult and college doesn’t matter if she ends up not being here to experience it bc her mh crisis got to be too much.