"That I was bringing the mood down. She said that if I keep telling myself I'm sick I'm going to talk my body into believing it. This turned into a lecture about mind over matter, and how my negativity was making me believe it."

Thats exactly how I spoke to my late mother about her fibro when I was healthy and now it has come back to bite me big time, call it karma if you like.

My GF has watched me go through this from day one and knows its real and is very supportive BUT her eyes completely glaze over if I even mention my pain just once so we never talk about it but I know first hand that its as boring as hell to healthy people.

I dont think your mom is a bad person, she just doesnt get it.