Has anybody else had this with their dogs?

I just got an older dog not sure of her exact age 13-16yr old carnie terrier. I have only had her about a week i took her to our vet to get her rabies shot and a check up sadly they told me the lump I felt on her was breast cancer we are going to go have a chest xray done to see if it has spread to her lungs. the vet said her heart sounded great for a dog her age. she runs around like a pup sometime and eats and drinks normally and potty time is normal. my question is i heard that a natural diet may help and i was just wondering if anyone else has tried that type of diet. oh she is only 20lbs if that matters thanks