I have my legs back under me where they belong, pardon the pun. After a long chat with our vet, I'm convinced that giving Phoebe a chance to live the rest of her life as a tripawd is the only clear choice.
The way it was explained to me is that as the cancer grows, it's essentially making the leg bone explode. You know how you curse to high heaven when you get up in the middle of the night and bang your shin and it hurts like hell? That's the pain Phoebe would have to deal with every day, 24/7. For the time being, she's on pain medication that's working well... but there will come a time when it's not enough. And when that happens, there are no other options -- no increased dosage, no other medications.
Her lungs, heart and blood tests are perfect, so I've made my decision to take the leg. Now I just have to convince the other half.