Ooh my, this sounds like a tough one.

Ooh my, this sounds like a tough one. Migraines or no, you and everyone else is expected to complete their work. Being a little quieter/less social is normal behavior sometimes so I think that the assistant was a but sensitive that you didn’t greet her with a pleasant ‘good morning’. On the other hand you’re supervisor gave a task to the assistant which isn’t her role and this is a bit tricky, bc if she has too much work and can’t complete her task or simply won’t complete the task than it all falls into a very gray area. You’re supervisor really needs to address this while you, need to get help for the migraines and (perhaps) seek out a better work schedule/environment. Your health is paramount.