It is looking like things have hit another major down point with my fiance, and I am hoping folks out there have some good advice!

When she is stressed, my SO usually shuts down, and I hear the "Go away and do your stuff" line, which is what happened last night; a bit of background to all this, my SO's mother is in Stage IV cancer, which her family (and her) are not doing 100% with (father not going to therapy, her 18 yr old brother trying to deal with issues, and the relationship with the mother was not good to begin with for any of them - suspect she may be BPD as well, but I don't have a lot of details as to what happened at their house growing up). I had a sudden work trip come up yesterday that has a lot of pressure surrounding it to see it get done; i tried to make arrangements for myself to leave today and be back in a couple of days, since my SO is driving 6 hrs one way later this week to pick up her brother to give him a break and get him out of his stressful house. At first, she was OK, but things snapped in the afternoon - why can't I leave on Wednesday, she is under a lot of stress (work, need to set up guest room, etc.), all she needs is one day (she has done this in the past with other trips and visits I have made), I am just trying to get away and leave her (turns out arrangements didn't pan out and I am leaving on Wednesday anyways). I tell her I understand her feelings, that she is very stressed and feeling hurt by my leaving on short notice, and tell her that I will work on the guest room before I leave and after I come back so that things are ready when she returns on the weekend (originally was going to just meed dad halfway in between where everyone lives to pick up brother but now they want her there for three days to "visit" and probably help "fix things" between them - since the cancer diagnosis she has become the new "mom" for everyone, including her father). After working on the room for a bit I come out to ask what she wants for dinner; I suggest something pretty simple that I can make quickly since it is a bit later and we are both tired from working on stuff on the weekend. I am told that I can eat that "crap", and that this just shows that I don't "get it", and that I don't care; I don't realize that she is coming apart emotionally (dinner is a bit of a trigger - she likes to do a lot of scratch cooking and expects the same as a sign of affection; I can swing it most nights, but not last night. Lately with the cancer news I have had to do more cooking and decision making, since she shuts down more frequently). Since then, she has been telling me to constantly go away when I approach her or even in the room when she walks in, and whenever I try to say anything to her she puts her hands over her ears and winces like my voice is causing her physical pain. With my leaving in a day, and coming back while she is gone, and then with her brother here (she puts on a face for family and friends, but still shuts me out - also, every time he has visited she has stressed to the point of shutting down with me for days) and staying for at least a week I am very worried and scared about having this continue for weeks. I don't know how to make things better for her while trying to do my work and keep myself rested. Reading about BPD I know I have to be the emotional strength in the relationship and provide some structure, but I don't know how to be 100% on 100% of the time and find a way to take the emotions and pressure off of her so she does not shut down like this. She is going to a therapist through her university to deal with issues with her mom's cancer, but her next appointment is not for another week, and she has limited appointments as a student and I am feel that talking to her about it that they are just offering band-aid solutions rather than guidance that can really improve her situation.
Can anyone offer any advice? Have you gone through something similar?
Thanks everyone for listening!
