[oh8eleven]

Right after the last surgery 2 weeks ago, a new tumor grew out and won't allow the paw to heal.
That's probably going to recur again and again and the Vet's bills will get way out of hand.
As tough and emotional as it may be (and since you did say she was a "senior"), I suggest it may be time to say goodbye.

[NCDave]

That is why the amputation is needed. To keep it from coming back.