Hi, 2faded, and welcome to the family! I am sorry for the reasons you find yourself here, but glad you found us. I too found myself safe here, it is a nice spot full of friendly people and I have seen tremendous healing happening on these boards.
It is great that you are in therapy already. It sounds to me like you had an abusive childhood and for that you need professional help. The more so if you are newly married - congratulations! Therapy will help you untangle your PTSD and leave you more emotional space to feel happy in your marriage. And that is your priority at the moment, not your abusive sister whom, thankfully, it looks like you escaped.
For now, it sounds like you are OK. She doesn't want any contact with you, then leave it be until she contacts you. You reacted well to the abusive messages, indeed you did right to enact a boundary and make it clear that you were not available to be abused. Leave well enough alone. I hear you are not up to telling the full story of the weddings, but it sounds to me like she is jealous and is acting out. Plus she is used to using you as an emotional punching bag. When she does contact you, you can come to us to advise how to proceed. In the meantime focus on yourself and take care of you.
Untreated BPD combined with substance abuse almost never goes well. She has to overcome the substance abuse before she can even get to the BPD and it is a long road. You might also look to joining AlAnon who provide support systems for families, so that you can grapple with how to deal with her alcoholism.
Keep posting, it helps to share. Many hands make light emotional work
