Who's first?

You are!

If nothing else, you can use your illness as an excuse for some of it; just say that you are too tired for any public get-togethers.That should work for a bit, maybe long enough for you to fell better and more able to deal with her. Also, you might want to think about the fact that, if it comes down to LTD, the informal meetings MIGHT be held against you.
Another thing you might say about not meeting with them is that your Dr wants you to rest, and not go out more than you have to.

I'd go anyway & suffer through it but look where that has landed me :)

One thing I discovered is that usually, someone in management at your employment has to fill out part of the LTD paperwork. Find out who that person is. You definitely won't want them gumming up the works for you later, so be nice to them. If it is your boss, you still don't have to (and really shouldn't!) have lunch with her. But you do want to make it clear that your poor state of health stands in the way, so very sorry.

And, for that matter, the others. Yes, it's good to get out. Yes, it's good to maintain social contacts. But if you are ill enough to stop working, you are also ill enough not to be expected to shower and dress and go out to meet people. If they care about you as you say, they will understand this. And if not, they're wasting your time and precious energy satisfying their own curiosity.

Just TRY not to say, "I'm too tired." They don't understand that - or rather, they think they do, and it only makes things worse. Just say, "I don't feel well enough to go out, but it's sure great getting to visit by phone, blah-blah-chummycakes. So what's going on with you?"

An office chum might visit you at your house if asked. A real friend will help you clean it without being asked. BIG difference. Painful as it may be, this is a time when you have to mentally separate casual and professional acquaintances from true friends. You can do it yourself, or it will be done for you by circumstance and experience. We all go through it, one way or another. Expect some serious "ouch", and remember to come back here when you get to one of them. We do get it. That's why we're here, actually.

Understand that if you are considering going out long term, that is a legal proposition - NOT a social occasion. A 'friendly business' turns into a 'strictly business' real fast. Their goal is a quick return to work. Your goal is to recover. However pleasant and polite everyone is about it now, you are severely at odds in terms of goals. And the insurance carrier? Not even close! Keeping that in mind, the last thing you want is for business and personal opinion to trump you and your doctor's intentions. So don't invite any extra scrutiny. These people aren't there when you go home and collapse for 3 days afterwards, and most won't be insightful enough to imagine it, either.

Even a failed attempt at a partial return to work can be used later in an attempt to discredit your claim. So don't even think about it unless you're 100% and rarin' to go. If you do go back, 3 months isn't an office pal killer. And if you don't, then you will have avoided potentially complicating your LTD case.

Disclaimer: I am neither a physician nor a lawyer. Just a claimant who's bt and dt. Found out I was very naive about these things. ( I have since recovered from that, at least.)

Having bt and dt too, I support everything Serena said.

If you can't say "no" on your own volition now, indeed 'circumstance and experience' WILL make the decision for you.

As you ask your question, part of what you're doing is "bargaining." That's an integral part of any situation where you're trying to have some control. Being in control of being out of control is key to any illness, especially this one that society doesn't believe. You've already done some good bragaining. You chose to leave work for 3 months. Continue w/ your bargaining. You done good so far! You pondered whether to take off for 3 mos., you decided to do it, and you found this place. Keep going ... you're on the road ... say "no" to coffee w/ the boss. You can live w/ yourself if you say that nicely, w/ mush. Can't you?

I agree with the others about definitely saying no to having coffee with the boss. You are ill and don't have the energy. Let those other true friends from work come to you. But I learned from experience, that you need to think carefully about who are true friends and which friends might take information back to your boss intentionally or unintentionally that will negatively affect your future claims for additional time off or disability benefits. I was a teacher with a bad principal/boss. She used any information she got from colleagues to discredit my skills as a teacher and would have terminated my teaching position, if I had stayed longer. I chose early retirement because I could and it was a the best financial choice at the time.