I would not worry at all about this puppy not being picked, honestly. You already said your friends not a breeder but now has the responsibility of finding good homes for these pups. I'm sure the people who already picked their pups out were attracted to certain things on the pups that they
liked. That does not mean this pup is defective in any way
She is a very cute pup, looks happy. The spot on her elbow...not sure? My first thought was maybe from laying on a hard surface? That is a pressure point area when they lay down.
If you do decide to take her you have to bring her to the vet anyway for a wellness exam. The vet will want to check her heart, ears, weight, mouth, etc... and will want a stool sample to rule out worms which is common in pups.
Stick around the forum. There is a lot to learn here and we all like sharing our German Shepherds with everyone.