Trigger's tumour was at the very top of his leg, and as it grew he struggled to move - he lived for two months after diagnosis, and on warm days (it was September) I used to carry him into the garden, where he basked very happily in the sun
in October the weather turned colder, and he took up residence in the top bed of the cat tree, where I used to bring him his food - he never lost his appetite, and it was a good place to make lots of fuss of him
part of keeping him comfortable was daily Metacam, and no vet visits once it was clear nothing could be done for him - he hated being put in a carrier so that was an important part of managing his last days
it sounds as if keeping Bass from moving around as much as you can might be helpful, and if she enjoys being outside finding a special place for her would be good
a brain tumour will not affect her digestive tract, I assume, so you should be able to feed her whatever she likes best - Trigger loved liver, and even ate a bit whilst the vet was here to euthanize him
I do think too it's important that you know her days are numbered, but she doesn't - she only knows how she feels on a day to day basis, so I wouldn't for a moment feel you need to do anything she doesn't like even if it buys her (and you) more time