Family Member Forced to Release Medical Info

I had to take 3 days off for a family emergency concerning my mom. She is fine now, but my boss is saying I absolutely have to fill out an FMLA form instead of use 3 of my 20 vacation days. My mom doesn’t want any medical information released, but my boss says she is legally obligated to release it because I’m obligated to fill out the form. I don’t think this sounds legal, as we all should have a right to privacy! I’m gonna get fired if I don’t complete this form and I’m hoping I can take my boss to court over this. I have a text and email trail showing our conversations.

IS THIS LEGAL OR NOT?