Large Inoperable Tumor

My mother who is 54 years old, has been having certain problems communicating for probably the last year and a half and she kept a lot of things, as far as emotions go, to herself. Everyone suspected that because of that, it was an emotional thing due to what we've been through in the past two years (our house was flooded and destroyed, we lost my brother, my aunt passed, friends passed, etc). Last Summer she thought she might have had a stroke. She didn't have any loss of strength or slurred speech or anything that made her weaker in any way, so she never mentioned it to her regular doctor. We moved once again into a perminent home, life went back to normal in the new place. She still had trouble communicating but there was no other problems. up until at the end of April of this year, she had a memory lapse for four hours. She worked through it and a few days later, had a little more problem communicating. She mentions that she knows what she wants to say but sometimes, when she gets to a word, she goes blank and she can't say it, even though she knows what it is. Her boss took her to employee health and that was that. She wasn't allowed to come back to work until she got an MRI done and checked for stroke. In the time it took to get appointments and such, she got off of Cymbalta which she admitted made her think more clear. Even after, she had one tiny memory lapse that a doctor later said could have been a mini-seizure. It only lasted for a minute and then it was gone. She got a call two weeks ago saying that she needed to be in the hospital because she had lots of swelling on the brain. She went in and underwent tests and later that week, a biopsy. They ran through the possibility of infection to possibly anything else. It was the size of a baseball they said. Every doctor was surprised to see that she had no headaches, no problems walking, her strength was good, she thought, for the most part, clearly, and she could function completely normal despite the swelling and the size of the mass. 

After the biopsy, the frozen sample, they said, looked like Anaplastic Astrocytoma. The doctor told us that it was slow-growing and that despite that, it could come back as a grade IV on the perminent due to how big it is. He also mentioned that it was too deep to cut out and in a bad place (left-frontal lobe). He said realistically, she may have anywhere from maybe a year to five but reminded us that they still didn't know for sure. They sent her back to her room and she came out of anasthesia quickly and was doing good and thinking clearly and communicating better. They sent her home the next day and she decided to stay with my uncle's until the perminent results came back. Tomorrow, she gets those results and she's so nervous right now that she mentioned to me today that she didn't think she'd be able to sleep. She is scared of what it's going to come back as but admits that there's nothing she can do about what's there except just go through treatment and fight it. It worries me that she's worried. The other doctors including another surgeon and the man who will be her radiologist and even her other neurologist seem optimistic given how well she's handled things so far. They've told her that no matter what it is, for her not to give up because they've seen people who shouldn't be living, live for years after and even still going today. While that is comforting to an extent, the only person we've had in our family that had a brain tumor was my brother and he gave up quickly. We tried to keep him positive but he just wouldn't let it seep in. He passed of a grade IV Astrocytoma almost exactly two years after he first started having symptoms. Of course, he was actually way worse off and his tumor looked better according to doctors, than mom's does right now which is why, I think, they're shocked she's doing so good. 

My question is, should I put much stock into survivability time frames? My mom and I got to talking and she wants to see my fiance' and i get married and have kids and she wants to watch my nephews grow up and she seems ready to fight this, whatever it may be comfirmed as, but she's worried that she won't get to.