Wow I am so sorry to hear what you are going through. It's an incredibly painful thing. Your mother has probably known for. While that things were bad - on an inherent level, though it's hard to accept on a mental one. This is probably her time to come to terms with it. Pushing people away is part of that. Sometimes when you are very sick - you just want time to wrap your head around it and you may not want people looking at you knowing youre unwell, and maybe feeling sorry for you, especially after all she's been through already. This may pass, some people get very angry to. It's all a part of accepting it. My mom was told the same thing she'd been given a very poor prognosis from the outset 5% survival rate - lung cancer - and it does respond well to chemo - she did the treatments and some radiation and was good for another 3 years, but lung cancer is cruel and tends to move up to the brain and it did - she was diagnosed with six tumors. Once that happened they said go home and enjoy your time with your family. We told her we weren't going to give up the fight, and were thinking about transferring her to PMH (the cancer hospital I was treated at) but she ended up with a bowel perforation less than a month after was in the hospital and became septic and died within a week. It was a blessing in some ways as she didn't have to suffer with the brain tumors. But heartbreaking for me and my step dad.
I am not sure how long your mom has. only god knows and he will take her when he is ready. Until then spend as much time with her as you can, despite her pain try to make it a good time, and not let this diease rob you of that. Give her a little time and see if she'll let your sister visit. The night before my mom ended up in the hospital she had come over and we'd had a nice family meal. That evening when She arrived. I looked at her getting out of the car and knew that she wasn't going to be here with me much longer. To be honest I still miss her. She was my friend and my mom. Make your final days with her peaceful and not about the cancer leave that in the background. Hugs and much love to you - I know this is a horribly painful time.