Thanks so much for the responses. I'll get her to the vet and request a fine needle aspiration as soon as possible. I'd be devastated if I left it and it was something more serious. She is, of course, my best mate!
I felt sure there were other alternatives rather than operate to remove it and now I can confidently go in and make the request.
The little darling was on snake alert yesterday while I was at work. Luckily I have a great neighbour who collected Doris(after hearing her barking madly at a snake on the front step) and let her hang out next door with her two little kids for the arvo Thank goodness for good neighbours (and a dog who seems to have enough sense to bark loudly from a safe distance rather than attack the snake ...)