HI rainedbows,
Welcome to the BPD Family
I'm sorry to hear how confusing and hurtful your mom's behaviors are for you It sounds like there is a lot of pushing and pulling, and triangulation with your sister going on.
Have you done much research on BPD? When I first found out about BPD I hit my local library and read everything they had, I found it really helpful to get a good baseline understanding of what I would call the mechanics of BPD... .what BPD is. As much chaos as it creates there actually are patterns to the behaviors. You'll see it here when you read the stories of other people and they sound so similar to our own.
Below are a few titles that I liked that you might want to checkout if you haven't already... .
Overcoming Borderline Personality Disorder: A Family Guide for Healing and Change by Valerie Porr
Surviving a Borderline Parent: How to Heal Your Childhood Wounds and Build Trust, Boundaries, and Self-Esteemby Kimberlee Roth and Freda B. Friedman
Understanding the Borderline Mother: Helping Her Children Transcend the Intense, Unpredictable, and Volatile
Relationshipby Christine Ann Lawson
I also wanted to share some information with you regarding the Karpman Drama Triangle because it sounds like from your story that you, your sister, and your mom may be experiencing this, below is a link to more... .
https://bpdfamily.com/message_board/index.php?topic=108440.0Again Welcome, I'm glad you decided to jump in and post. I know other members will be along with more feedback and ideas for you.
Take Care
Panda39