Hi and welcome to DWD.
It does sound like it's blown up over something simple. I assume you've removed her from your friends list? All this over you adding her to FB?
You've several choices obviously - smile and ignore and continue as you are, leave, or talk to your friend and explain..... The issue is that it's having quite massive effects on you and your health. Is it worth going to see your Dr, telling them what you've told us and explain the effects that it's having on you?