I'm so sorry. Your mom has what they call "high load" stage 4 metastatic cancer, vs "oligometastatic" stage 4 like my prostate cancer (just one known metastasis, though it did a lot of damage to my spine).

I don't know much about modern breast cancer treatments, but for prostate cancer there are many new treatment options now, even after it spreads like that. None of the treatments is a picnic, though, and many increase the risk of other conditions like heart disease or diabetes.

I was 56 at the time of my diagnosis and mostly healthy (except that the cancer had left me temporarily paraplegic), so we decided to "throw the kitchen sink" at my stage 4 cancer. So far, it's doing the job and I feel I still have a good quality of life as well as quantity. Treating her cancer with "curative intent" could buy her more years as well, but it could also make her sicker, especially if her health already isn't great.

As others have mentioned, there's nothing wrong with choosing palliative (focus on managing symptoms) over curative (focus on fighting the cancer), or vice-versa. This is a decision she'll have to reach after talking with her care team and family.

Best wishes.