So sorry about the situation with your sister. It seems that many of us reach a time with our BPD, uBPD, when we have to limit or discontinue some form of communication. Either temporarily or permanently.
I'm only communicating with my sister by US Mail right now. My sister won't admit she has a problem and refuses to get counseling. I reached a point, that I just couldn't bare to go another round, without talking over the issues and pretending that nothing happened and wait for the next episode, and the next and the next after that.
For a period of time, I just ignored the texts and emails; but, it can be unnerving to just get a text, because if you have a text alert on your phone, you have to at least dismiss the alert and usually see some of the words. I finally blocked my sister from texting me. I went for a period of time, when I ignored the phone messages, then I blocked the phone calls.
If you don't want to block her emails, you can direct her emails to automatically go to a special folder. I'm using gmail and I disabled the preview feature, so I only see the from and subject.
Once you learn how to block someone on your particular phone, it is easy to engage that feature and then reverse it. One option is to engage the block feature when your sister initiates a text bombing episode. You can then easily reverse it if and when you want to, when you think the time is right (or leave it blocked).
It seems that most of us reach a time with our BPD, uBPD, when we have to limit or discontinue some form of communication. Either temporarily or permanently.
I'm still learning about boundaries. Here is an address to some info. on boundaries on this website:
https://bpdfamily.com/message_board/index.php?topic=61684.0
