I’d focus on her health. College will be there when she’s ready- and if she’s truly vacillating between “I can focus on this and do well” and “I don’t want to do what I don’t want to/can’t do” college is going to be an anxiety provoking experience for her all around.
There are all sorts of workarounds for kids like what you’ve described. I’ve seen kids take one class at a time at a community college, for example- while working and living at home- and after two semesters, are able to tackle full time college with much improved work habits, less scaffolding from the family, better appreciation for the reality that not every course is going to be totally absorbing all the time.
I don’t think there is a hard and fast rule about revealing ADHD, but no college wants to admit a kid who is going to struggle, for whatever reason.
How does her anxiety/depression manifest itself and what does her therapist think?