Sometimes a steroid will help slow a tumor's growth- I have a rat on prednisolone for that purpose currently, and the other one I've heard about being used in rats is dexamethasone. Ask your vet whether they might help!
How old is Mochi? If you're not planning to have rats over the long term (so that a revolving door situation would be okay) then Mochi might be okay as a solo older rat if she's getting plenty of affection. Of course, that depends on her temperament; some ratties get mopey if they're alone.
How old is Mochi? If you're not planning to have rats over the long term (so that a revolving door situation would be okay) then Mochi might be okay as a solo older rat if she's getting plenty of affection. Of course, that depends on her temperament; some ratties get mopey if they're alone.