7 year old GSD pregnant by 9 month old GSD?

I just rescued a 7 year old female GSD from a neglectful owner. A week after I adopted her, I took her to the vet for a check up (I had made an appt. for the following week to get her spayed). We had assumed she'd been used as a breeder in the past, but did not seem pregnant. The vet felt her abdomen and thought her spleen seemed enlarged, so an x-ray of one of her sides was done. No spleen problems Thank God, but two puppies showed up on the screen. The vet said she was about 45 days pregnant. I canceled her spay appt. immediately, but I am wondering if only 2 puppies is normal given both the dam and sires ages, or are there probably more puppies than we could observe? I have no experience in this matter, as both of my previous dogs had been spayed before they came into their first heat. I hope someone can share some insight as to what to expect, and whether or not 2 puppies is normal in a situation like this. She is due any day now, I just hope everything goes smoothly.