@frieda909 she really hasn't had a kicking on this thread. Most people have shared similar experiences and cautioned her against making a mistake which could cause her lots of problems. And it is true that many people will feel that too ill to work includes teh Christmas party just ONE week after she has been signed off. It sounds as though she is going through a very tough time and the vast majority are saying, not with judgement but with experience and concern, that teh Christmas party is not a good idea.
OP i would also be worried that the reality of it may not be as you are imagining. From having such a severe breakdown as week ago, I, kindly, wonder if you are over estimating the support of work and camaraderie. I know when I have been unwell i have lost perspective on situations and people somewhat.
I am sure that those of us telling you to make other friends are annoying. It is bloody difficult. But dont see it as making bosom buddies, maybe as just getting out and meeting new people. I am sure this is a silly idea but would a fostering or adopting a dog be possible. I have met many people since getting a dog. I talk to people everyday. They aren't my friends, but are other dog walkers. Some of whom i have swapped numbers with so we can organise walks together. Also having a dog makes me get out every day and get a good amount of exercise. And he gives love and affection. It is expensive though and a long term commitment so i am not sure if it is possible for you right now. Alternatively you could look at borrow my doggy if you like dogs but cant commit to walking.
Have they reviewed your medication? Are you involved with a crisis team? Do you have any plans for Christmas? It is such a hard time of year. Maybe if you have no family near to spend the day with, it would be a good idea to contact a soup kitchen or homeless charity so you aren't at a loose end on such an emotive day. I'm sorry if any of these suggestions are facile or silly. I can hear that it is tough for you and just chucking a few ideas out there.
One foot in front of the other, you just need to keep moving forward even if it is at a slow pace. Just concentrate on teh next minute hour day. Break it down as small as you need it to be.
Good luck.