Resources to help my mom recover from her family?

Hello all. I hope this situation is relevant enough for this sub, because it's the closest I've come to finding people with the right mindset. I'd be really grateful for your help.

My mom (60) is doing an amazing job unpacking her family issues in therapy. She grew up with a parent with severe, secret mental health issues in a really repressive household, and neither she nor her sister came out of it doing well. My mom is too self-sacrificing, and quite fearful, and has a deep need to over-explain herself so people don't get upset when she tries to maintain any kind of boundary or her perception of reality. I personally think she has PTSD from this family situation, though her therapy is not that far yet.

My grandparents have both died several years ago now, but my aunt is still alive, and the relationship between them is very strained. My aunt is not okay. We dont know exactly in what way. NPD, ARD, cluster B, PTSD? But she's got very apparent mental illness issues for sure and it's hard and sad. My aunt does not have any people she's really close to except sort of her 2 kids who are young adults and have had a hard time dealing with this also. My mother feels bad for her being in pain and lonely, and is really used to trying to manage other people and keep the peace. However, the contact my mom has with my aunt is erratic and taxing and easily turns emotionally hostile, it's rarely ever positive. It triggers a lot of bad feelings in my mom, and she's had to go to the doctor for heart medication several times now and even to the hospital once because of a health emergency immediately after contact due to the stress of it. It has me extremely worried.

With help of her therapist my mom is trying to go low contact and grey rock, to untangle herself without much of a confrontation, and she's been doing well at that in practice, but she finds it very emotionally difficult to not try to help and spends a lot of time worrying about my aunt's well-being (not good) and about upsetting her (likely) anyway.

I have been looking for resources for her, and her therapist is great so that's a big important resource and help. She's gotten recommendations from her, but they're limited to our native language, and I'd really love to ask here if people have books or even articles in english that have helped them deal with a mentally-ill, self-centering family (member) from the position of solely trauma recovery and self-care and low to no contact specifically.

The stuff I'm finding all has stuff like 'how you can best help while keeping boundaries' and 'it helps you to try to understand their diagnosis' and 'they may not hurt you on purpose'. I don't want my mom to spend any more energy (or her own health) helping or analysing my aunt. And my aunt doesn't have a diagnosis. It's hard to say why she acts the way she does. Regardless of her intent or control, and I do feel very sorry for my aunt also, she's unwell and in pain and I wish she was not, it's imo become dangerous to my mother's health to be involved further.

I really am hoping for resources that are focussed on my mother's well-being entirely, and how she can find her peace in this complicated situation with so many unknowns, and learn to stop self-sacrificing. Not advice that is partially focussed on her managing my aunt, or putting herself first but my aunt still second, or analysing if my aunt is awful or sick or how much of which.

From what I've read in this sub this is a route more people here have been forced to take, and I'd love to know if you have resources you'd recommend in this particular situation. Truly thank you very very much! I'd appreciate it a lot.

(I made a new account for this post, but I'll be reading all the comments. Thanks!

And lastly just btw if people wonder, I've ended up pretty okay myself at this point in my life, so that's nice. :)

I hope you all have a good day.)