My German Shepherd puppy is confused. I'm trying to use spatial pressure to teach her to back up and she lays down instead.

At 15 weeks I might simply take a break on working on back up for a bit. Sometimes simply taking a break from things like this and rethinking reward placement will help. Using spacial pressure on a really young pup often confuses them.

I've trained a few puppies to back by doing a couple of steps: I create a channel for the puppy so they have to move straight back. I then get down on their level and since my puppies already understand to move away from my closed hand that contains food the very moment they take a tiny shift back I mark it and toss the food with my other hand under them so they have to back up to get it. I think Ann Braue may demo something similar in the course you have ? I haven't watched it in a while so it may not be exactly as I described but it might be worth reviewing.

Thanks so much for the kind words and for your business. :) Let me know how it goes with your pup.