I am too, Sabis Mom; it's funny how many horsefolk there are on this forum.
The kind of movement that you've described is considered interference in horses. Arguably, it's the same thing in dogs. If I'm correct, that happens because the dog isn't strong or mature enough to carry itself correctly. (Barring physical or conformational limitations). So, it moves in a kind of overly rounded (aka hunched up) kind of frame. Mind you, this can be very subtle and hard to see without a lot of experience or a video that you can slow down. Also, my interpretation assumes that there's no structural or conformational restriction on her movement, so that the over rounding, so to say, is the best that she can do. (Again, consult your vet or a GSD Guru about this
If she's youngish (can't find where you said how old she is), it may be that she simply hasn't figured out how all the growing parts move and this is her way of adjusting. If it's just a question of immaturity, she may well grow out of it without intervention on your part. Even if it is only immaturity, you can facilitate things thru exercise to build her strength and body awareness and/or by helping her to strengthen her hind end and abdomen by gentle exercises that encourage her to elongate and reach in the front (e.g., spacing the cavaletti more widely) and drive better from behind (e.g., hillwork).
A final thought. Can you reach out to her breeder? Take her for a visit with the breeder to get another pair of eyes on the movement? Or, perhaps, take her to a nearby GSD club to get other folks to have a look? Or, failing that, make a video that you can post here for the forum gurus to have a look at? Movement's tricky enough in person or on a video, and impossibly difficult to interpret on the internet.