Mum cancer diagnosed a day before death

Hey, I just needed somewhere to post this as I'm struggling to understand stuff. I know I shouldnt really be thinking about the ins and outs but I cant help it. I live far away from where my mum lived but just before her death she was in and out of hospital. Then she went back in, she called me disstressed and a day later my brother called to say they think the cancer had spread to her brain. 

 

What I dont understand is how they can think the breast cancer was gone and then 2 days before her death find it in her brain. We got too see her in her final hour but it was an awful way to see her, dying. They said she was fine and then just started deterating rapidly. can this happen with cancer? no awareness until theyre nearing death.

 

Anyway im finding it hard to cope, I wish i had someone to talk to about the visuals of what happened. Is there any free help available to talk to someone about this? I cant help but feel angry at the doctors and replay the whole thing over and over in my head