Hi Mara Ashley

Welcome to our forum!
I feel like I am trapped with her. I feel depleted from her. I feel like I have had enough. Am I just drained and needing space, or is this my emotions telling me this is my boundary and to cut her off for my own sake? I know it is my responsibility to take care of myself. I try so hard. But when there’s a choice between making sure my sister eats that day and going to my yoga class, how can I choose the latter?
Mara you are describing feeling trapped and depleted. We are all different, and we don't have any details of your story here, but I can say that when I got to the point of feeling "trapped", I was very frustrated, and also feeling hopeless and helpless. I saw my Dr, and he was able to help me see that I needed to start looking after myself. He also helped me find other ways to support my uBPD mom. A uBPD mom and a uBPD sister are two very different relationships, but there are probably still similarities in the personal challenges we faced around feelings of guilt. Have you consulted with any professionals such as a doctor or counsellor? I found having that support and validation from a professional in my own community was a big help, and it gave me a boost emotionally, and provided motivation to move forward. This forum was equally helpful, and together they achieved more in clearing the FOG for me to see a way forward.
I’m just venting and complaining.
No you aren't. It's a complex and legitimate concern that would challenge an experienced person. Instead of thinking that you are venting and complaining, think of it as you being responsible in recognizing that it's a significant problem that is affecting your own well-being, and you are doing the right thing by looking for help to find the best way forward.
But she truly doesn’t want to get better and would admit to that.
Do you think your feelings of frustration are mutual?
At the top of the page of the Parent, Sibling, and In-law group, is the "How to Get the Most out of this Site" subject. There is SOO much good info there, that I have been on this site 6 months and still go back there to read and refresh myself on that material. Super helpful. I would suggest focussing on SET, asking validating questions, and boundaries, but you may find that once you start reading, it is hard to stop.
But when there’s a choice between making sure my sister eats that day and going to my yoga class, how can I choose the latter?
Since you are a twin, I am assuming your sister is an adult. We "non's" have been "trained" to feel responsible for our BPD's well being. But this is unhealthy thinking and feeling on our part. "They" are adults, and as such, they have autonomy to make their own decisions. We may be saddened or disappointed by those decisions, but the decisions are still theirs to make, and the consequences theirs to accept. Having said that, we can still support our BPD's by using SET and validating questions to ideally guide them to better decision making, but we may have to accept that they can still make decisions we don't like. We can also use boundaries to protect ourselves. Sometimes those boundaries may include LC or NC for some people.
Can you tell us more about your situation?