It sounds like your mother is confused about what to do, and about what will happen if she does or doesn't do chemo. You need to sit in on a thorough discussion with her and her doctors to make sure you have all the necessary info and that she understands her prognosis with or without chemo.
Women who live many years with stage lV are typically receiving treatment to keep the disease stabilized (can't cure it at this point). If your mother's disease is progressing rapidly, then she needs to either receive some kind of stablizing treatment (assuming it can be stabilized), or you need to start setting up Hospice arrangements.
From what you've said (not eating, massive fluid buildup), you don't have a lot of time to make decisions to slow the course of the disease. Is there a breast cancer advocate, a counselor or some kind, somebody to help your mother work through what she wants (quickly)?
It sounds like quality of like is a big issue. You need answers specific to that. If untreated, will she be in massive pain and are there meds to help with that? If untreated, will she continue to have massive fluid buildup? If untreated, can she eat?
Sit down with your mother and paper and pen and talk to her about what SHE is worried about, what SHE wants, is she being unrealistic, is she in denial, does she have a living will, etc. It sounds like you have been talking to her, but I sense a lot of ambivalence and confusion that needs to be cleared up, both at the medical and personal level. You need some specifics from the doctors to help your mom make some specific decisions. Good luck to you and your mom, and I'm so sorry she has to go through this.