First off, I am very sorry to hear about your dog.
Depending upon the type of cancer (was a biopsy done?) options for treatment differ. The basic rules are to make sure she is not in pain (anti-inflammatories, pain killers, prednisone) and make sure she continues to eat well. Keep feeding her a balanced diet but at this stage feel free to spoil her a little with extra treats.
Cliff, Thank-you for responding to my plea for help, no, a biopsy was not done and sent away for analysis, the vet said he could tell that it was a nasty cancer by the couple of very small incisions he made on her lumps, and it would be days rather than weeks/months before she would have to be put down. At first the vet was quite sure it was a grass seed that was causing the lumps, but on further examination on the operating table, he decided it was a malignant cancer, incidentally he said she turned very blue under anaesthetic and they had to quickly bring her round for fear of losing her. at the moment she seems to be panting on and off when our other dogs are not, she is eating very well, last night I was worried she had not been drinking water,, but my wife has since said she is drinking now. I have changed her from dry food to canned, and am basically following what you have advised in your message to me for which I thank-you very much. I hope to hear from you again.....regards Miles Dexter