Lucy - is her weight low?

Our rescue puppy, Lucy, is estimated to be 7 months old. She weighs 41 pounds. We have thought for a few months that she is on the small side for a GSD but this seems on the extreme side. Lucy is a Parvo survivor and was nursed to health in a foster home with other Parvo puppys. We were told her entire litter was probably abandoned once diagnosed with Parvo. Can Parvo stunt a dogs growth?

Either that, we are considering she is a mix with some other breed but for the life of us we have no idea as Lucy looks like a full breed GSD, just very small and dainty.

Any ideas or suggestions are appreciated. Thank you.