OP- huge hugs for you. Your pain comes through in every post.
A couple of suggestions (I will not repeat the other very fine, wise advice you have already gotten, some from posters we’ve all known for years, and trust me, they are experienced and battle scarred).
1- Get yourself counseling ASAP. You need a healthy outlet for your own complicated feelings- fears for your daughter, a sense of “what did I miss?”, etc. And keep your most empathetic friends and acquaintances close- I learned the hard way during a very tough depressive episode in my own life that some of my “best” friends were useless and some of my “not so close” acquaintances were absolute gems. And not just because misery loves company- but because people who have faced tough challenges are often much more sensitive to observing struggles in others, and can be there for you in a way that “closer” friends cannot.
2- Remind your D and yourself that virtually every assumption you guys are making about her professional success are just plain wrong. Competitive internship? NO WAY. Not necessary. Maybe down the line- but not now. Finishing in four years from the college she started at? NOT ANY MORE. Running on a treadmill to keep up academically? NOPE, not necessary.
You can thank Covid. All the “established” patterns have been broken, and companies are shifting as a result. Kids are taking time off for all sorts of reasons- it doesn’t reflect weakness, it reflects having a strong sense of self and reality. And honestly- if your D has been miserable keeping up academically, why on earth would she be choosing a career path that involves an internship certain to offer more of the same?
3- You may not love your job, and you may do it for the paycheck, but there are millions of people who love what they do (I’m one of them) and taking a Stoic approach (if she wants to support herself, it might involve some misery) doesn’t seem to sit right based on what you’ve posted about your D’s challenges even back in HS. I know people who teach autistic 4th graders who love their jobs (and are self-supporting, and paid back their undergrad and grad loans) and I know investment bankers who love their jobs, and I know police officers who love their jobs, and someone who does event planning at a large, high end hotel who loves her job. If your D is struggling to reconcile some of her high standards/need for perfectionism/need to prove herself by running a marathon in her head-- having her click with a counselor of some kind to rewrite her narrative might be really, really huge for her.
Consulting or Banking will still be there in a few years if your D decides to take a year off. (or whatever other high stress internship she’s doing). America is the inventor of Second Acts.
I have no advice to give you on the farming gig. I would also be massively stressed out if one of my kids was going far away before stabilizing-- but perhaps encouraging her to find something similar closer to home could work??? Surely the social isolation isn’t helping her, but there are other ways to find community besides going across the country-getting a job at a local farmer’s market? volunteering at an animal shelter? Teaching crocheting at a nursing home? Something where she’ll be surrounded by nice, non-competitive types where the work isn’t yet another test or race???
I do not have personal experience with NAMI but I’ve heard their support programs are life-altering (and life-saving). I do know that the meds take time… and think you’ve gotten great advice to get a physical done as well.
Big hugs. You can do this. Lots of us have discovered that the neat, linear plans we had for our kids got derailed and we’ve learned to cope/exist/eventually come to terms with the new reality.