Welcome: I'm sorry about your situation with your sister. As a BPD Family member, you will find a lot of listening ears and people eager to share and help each other. This is a safe place to share.
You can't change your sister, but you can learn to interact with your sister and manage your reactions in such a way to defuse situations and make life better for you.
Boundaries can be important for you and your mom. It's up to you and your mom to enforce your personal boundaries. Using Validation can make a difference, as well as various communication skills. Check out the links below (click on the green words or green addresses). There are, also, links to the right of this post, that lead to additional helpful information.
VALIDATIONCOMMUNICATIONS OVERIVEWSETTING BOUNDARIES The link below, leads to a list of workshops, in the Learning Center. Some topic might jump out at your to serve an immediate need. It can be helpful, to discover some of your learning options. Once you see a topic in the directory list, you can then go to the 2nd link below and find the lesson in the Workshop Thread.
DIRECTORY - SKILLS TRAINING WORKSHOPhttps://bpdfamily.com/message_board/index.php?topic=296645.0SKILLS TRAINING WORKSHOPhttps://bpdfamily.com/message_board/index.php?board=36.0I look forward to seeing you on the board. I hope your journey here leads to a good 2017 for you and your mother.