It turns out to have been a wise move, because she's developed heart disease, probably from the steroids that she's been taking to treat the cancer. Our vet was careful to say that our accidentally overdosing her on steroids for about a week was probably not a factor, but I don't know.... she may have just been being kind.
For the first few days at the vet, Bunny was nosy and demanded attention from everyone, even sticking out her paws from her cage to smack at a broom.
But she developed breathing problems over last weekend, and our vet took X-rays, discovered an enlarged heart and fluid retention around her lungs, and started her on three more medications. She's hopeful that these will stabilize the heart problems.
We're hopeful, too. She's clearly not herself, and it's very sad right now.