Sibling (31/F) with a rage texting habit - should I forgive?

My sibling (31/F) is bipolar, I am (34/F) with depression (but managing it). We were raised by adult children of narcissists (who may also be narcissists).
We have a close relationship and text daily, though she currently lives in Europe and I'm in the US. The problem is that our relationship can become extremely volatile at times.

Recently, the day before Thanksgiving, an argument broke out in my family because my mom, who was hosting Thanksgiving for my immediate family, invited her narcissist mother over for Thanksgiving. Having been the recipient of hours of my mom's complaining about her mother abusing her, taking advantage of her and otherwise being a horrible person, I took issue with this. On top of that, our other, younger sister got married last year, and my grandmother didn't rsvp, nor attend her bridal shower or wedding and still can't produce a valid reason why.

That said, my mom excusing my grandmother's behavior and having her sit at a dinner table with all of us rubbed a few of us the wrong way. I asked my mom why she would invite her and she said because she's family, that's what you do. So I said fine and ended it there.

Apparently my mom then texted my younger sister, who moved to London recently (our family lives in the states) telling her that she was having a horrible day and being attacked by me on this subject of my grandmother coming to Thanksgiving. I know this because my sister sent me a screenshot of my mom's text, and proceeded to rage text me for over 45 minutes, cursing, name calling and saying things like "you're a fcking bitter child living in an adult's body" and that I should learn to be "fcking grateful". I responded nothing but "please stop" and "don't you realize mom is manipulating the situation and you to be her attack dog" but it didn't do anything to end it. Finally I blocked her because I couldn't take seeing the texts coming in anymore. I didn't sleep and battled suicidal thoughts most of the night.

My sister apologized via email the next day. She basically said she was stressed out after her move and lashed out. I responded back to her that I needed to understand more about why this happens - and reminded her that it happened before in April and she uses similar terms like "f*cking immature child" and that also sent me to the brink of suicidal ideation, after not have felt that way for a very long time.

She responded again, this time saying she was just trying to protect my mom, and she gets upset seeing her sad. She then sent me her email and password to an online news account that she knows I like, and has sent me some funny YouTube videos (none of which I responded to, yet). She also said "please, can we stop the fighting. I don't want to fight." She did not acknowledge anything about what she said, or take responsibility for using the words she did.

I'm at a loss because I care about her, and don't necessarily want to cut her out of my life completely. I know she is a victim of my parents setting poor boundaries, and pitting my four siblings against each other constantly. I also don't want to drag out the argument and repeatedly say "that apology is not good enough" and take a rigid, defensive stance either because I don't think that helps. What I am sure about is that her behavior is completely unacceptable and I know I can't accept the apology without her acknowledging the behavior itself, and getting some indication that she's working on not doing this again. I have not gotten that and I haven't responded to her text.

Any thoughts on how to approach this would be greatly appreciated.