yeah, don't stress about that letter. If she wants you to read it; let her send it to you regular mail. Life is much too short. What Cat and Knot said.
I have always had a difficult relationship with my mother as well. Now her husband is dying and it's like dancing on a melting dance floor while holding little glasses of champagne in one hand. It's really really tough. But you do have to take care of YOU first.
To thine own self be true. What's the point of missing work to get a letter that's just going to make you feel worse?