Welcome Shrugqueen

This week her world has been turned upside down because I told her who I'm voting for in the next election.
So you're not alone. My 83 yr old mom wanted me to make sauerkraut with her, so I thought "OK" it's at least something active to keep us busy if we are together. But, sauerkraut needs to sit and ferment. My mom canned hers (well she had me can it) after the first week. When I said I was going to let mine ferment at least another two weeks she "flipped a gasket" and went berserk.
I have found there's a big learning curve to understanding BPD really well. Based on the example you gave of telling her who you vote for, and the consequence you experienced when it was different than her, I would suggest not sharing "personal information" with your mom. In my sauerkraut example, I came to understand much later that BPD's simply can't handle their SO's thinking differently than they do. It will usually cause an incident or rage. My mom gave me the silent treatment for 3 weeks because I decided to ferment my sauerkraut for the proper amount of time (4 weeks is recommended). After that, it was a very tentative slow recovery in our relationship.
We can't rationalize with BPD's. Back then, I tried explaining to mom why sauerkraut needed to be fermented longer. She had a total meltdown. Do you know about JADEing? It doesn't work with BPD's, even though we do it daily with non BP's, and the rest of the world functions on it (except for BP's). When you are tempted to JADE, don't. Here's a link:
https://bpdfamily.com/message_board/index.php?topic=280750.0I don't get to have my own opinions, not to mention boundaries! Even if I gently say, "I don't want to talk about it," she will fly off the handle
Yes, because you have a different opinion than her. I have learned it's better not to share opinions or personal info. Once I accepted that was the way it had to be, my life got easier.
Also, once I accepted I couldn't JADE, and actually stopped JADEing and started using other BPD friendly strategies on this site, my life also got better.
The hardest part is accepting it. We all want a non-mother like our friends have. But BPD mother's are different. Accepting that is a big step.