Pre-grief and overwhelming guilt

My grandma was diagnosed with Glioblastoma a few weeks ago. She's been in the hospital ever since she had a fall in the night and had to call an ambulance. They say it's very aggressive and she will likely only have a few months remaining which has come as a massive shock to me. The doctors have backed-and-forthed on whether to operate multiple times now. I suppose because of her age and where it is. At present they are saying they will try to operate on Monday which we're nervous about, but if it could extend her time she wants to do it. I know she's scared of chemo and losing her independence - with no one nearby to care for her she will likely need to go into a care home.

We've always been extremely close. I want to spend as much time with her as possible, but my car broke down on the last visit and I got caught in a snowstorm on the way home. I wish I lived closer or could stay closer but she lives remotely from the rest of the family (by choice). She lives about 5 hours drive from me, but we always tried to have a summer holiday together and spend christmas together. Despite promising to visit, I was unable to do so this summer. She kept asking when I was coming because she was lonely and I had to keep pushing it back for one reason or another. I felt guilty before all of this, but now I feel devastated.

She's still here, but it feels like I'm already mourning her and I can't fathom how I will feel when she's gone. She's my go-to person. I will try to visit her this weekend (weather permitting), but I don't think I can stay to keep her company on her operation day. I feel wretched about that too.  I'm reading my own words and feeling selfish because she's there alone.