Welcome SD Suzi : Sorry about the situation with your DIL. You aren't going to change her. Things never go well with interacting on Facebook, with someone with BPD traits. If you ever disagree on anything, expect a poor outcome. If you always agree with her position and validate her, then things might be okay. Best to find/use different social media options that don't involve your DIL. Consider developing friendships with people from church, where you can talk on the phone, email each other or have them to your home, etc.
You can't change her. Your best approach is to learn various strategies and communication techniques to change the way you interact and react. The strategy at the two links below can help you avoid arguments:
AVOIDING CIRCULAR ARGUMENTSbpdfamily.com/message_board/index.php?topic=118892.0;all
KARPMAN DRAMA TRIANGLEhttps://bpdfamily.com/content/karpman-drama-triangleYou and your husband will need to combine efforts. You will never be able to debate politics around her, or discuss opposing views, like you may with people without BPD or strong BPD traits.
The skill of
VALIDATION can be a helpful. Click on the link and check out the article.
Take some time to check out some communication skills and share them with your husband. You don't need to block or unfriend her, but you will need to show restraint and do not JADE (justify, argue, defend or explain). If you don't have something nice to say, stay silent. You might want to consider starting a 2nd Facebook Page, where you can interact with people outside of your DIL's circle.
let us know what you think about the JADE strategy and the Drama Triangle. People with BPD can have a strong reaction to being invalidated.