First of all I totally sympathise with how worried you must be about losing her. I've had my dog for 5 years and she is my best mate. I cannot imagine a day in my life without her.
However I do want to stress to you that taking her to the vet is the best option. Not only will it determine what the actual lumps are BUT they also could provide your dog with medication if necessary. Imagine if she is in pain? Wouldn't you want her to stop hurting? Best to have her checked out immediately, and put your mind to rest.
I often wonder to myself that I would be heartbroken if my dog were to die accidentally or tragically. But if I get the chance to have her in my life and her die of an old age, then even though this will still upset me greatly, I'll at least be grateful that I had her all her life and that I provided her with a loving home. I know your dog is getting older, and unfortunately death is inevitable. It is the worst thing in the world losing a pet- its like losing family. They become our family, a huge part of our lives.
I really encourage that you have her checked out. It wont cause her any more stress and if she is in pain then at least they could possibly provide medication that may ease this.
Good luck with everything and may your pooch have many wonderful years left!
P.S Its great to hear that there is nothing different about her behaviour, eating or sleeping habbits which is obviously why you haven't stressed about taking her to the vet. The dog I currently have, I had her mother for 12 years and she developed a few fatty lumps. But at least by taking her you have peace of mind? You know your dog better than anyone, so its your call :)