Lumps and Bumps on my Cat. Is it serious?

Before I ask I know what half of you will say: Take it to a vet. My problem is that my mom won't take my cat to the vet unless she thinks there's a chance of it being dangerous and my vision is too bad to drive by myself. My female cat is pretty old and the vet thinks that she is somewhere between 10-15 years old (we found her on our doorstep). She has always been sensitive about anyone touching her belly but I found a growth near her a month ago along with several bumps underneath her skin. These don't seem to be growing bigger and aren't bothering her. She also has a large bump in between her back and where her tail starts. She gets very irritated if you touch it. Do any of these sound like something that could be serious. I'm really concerned about her but my mom isn't.