Brain metastasis survival rate

So my mother was delirious a couple of weeks ago and they found a metastasis in her brain. I’m not quite sure where, as I don’t have the paper at hand.

They released her from the hospital after two days, but they didn’t seem to be too worried about it. They told me it’s very small.

So I made some research and found out the survival rate is EXTREMELY low. Things don’t add up. Why were the doctors so calm about it?

I’m only asking here because I don’t really want to talk with my mother about this. She had breast cancer, if that can give you a better idea about what she’s facing.