Has your vet told you what type of cancer it is? There are a lot of options these days and depending on the diagnosis, your girl may do well with a number of them. From your description of her, she sounds like she is loving life so her age may not be a factor. There are a lot of knowledgeable people on here so if you can clarify the type of cancer, her age and what your vet has recommended that would help us help you.