My 4 month old 16" and around 25 lb Shep pup, Nadiah, seems to small to be GSD...any suggestions about what she could be??

She just looks like a puppy GSD to me. You said she's 4mon old, she still has some growing to do and could just be a GSD.

4 months old puppy can hard to distinguish its breed...
When a she reach 6 months...
There you can see much changes and you can easily distinguish the right breed...
That's what happen to my dog...
We thought that he is a Shih Tzu...
But now that he is 6 moths old...
His real breed came up...
He is a Japanese Spitz mixed Chow Spitz...