I'm going to be 100% honest here, because anything else won't let me sleep tonight.
I'm glad you're happy you got your GSD and that she seems to be listening to you so far. However, I have serious misgivings about this whole situation and about the honesty of the guy who gave you the dog in the first place. Something about giving a "protection trained" dog to a young person who has no idea what they're in for sits wrong with me. I have to say my first impression is that this is a poorly bred GSD with snappy nerves and the guy was looking to unload her...those feet aren't just huge, they're "wrong".
And please, please, PLEASE DO NOT set your baby down on the ground in between two dogs who don't know each other! I want this to turn out well for you and I really REALLY don't want to log in one day and hear that your baby had to go to the hospital and the two dogs to the vet because of something like that.
Enroll in an obedience class immediatly. Not for the dog, for you. You have to know how to handle what you've set yourself up for.
Best of luck.