My 9yr old GSD had a mammary tumor. It was found when she was about 2-4 (don’t know her true age, the vet estimated 2-4 when I got her). At that point, it was not causing any discomfort or pain, and was benign. At the age of 9, it started to grow and become uncomfortable for her when she would lay down. We had the tumor removed and had her spayed. She’s doing great! I know it’s much easier to say than do, but don’t stress until there is something to stress about!
My girl had been a BYB breeding bitch prior to me getting her, and she had been bred at every cycle, including her first. The vet couldn’t tell me if it was the litters that caused it, or her not being spayed. Why take the chance? She’s past the age of maturity for a female GSD. I’d go with the spay.