That is good at least the Black Salve is made for animals. But because I know how it acts, I would be still hesitant to use it if the Tumor has spread to the belly and lungs because it will follow the Tumor line and be too painful in those areas. And I would also be hesitant because of her age.
What Dq suggested is good, and what lolite suggested about Essiac is really good, I forgot about that.
Cats are so picky you will have to give stuff to her with a pet feeding Syringe. Here's what one looks like, Easy Feeder Hand Feeding Syringe, scroll to down to bottom of page: