German Shepherd - training Regression

Question
I adopted a 6 month old white German Shepherd from a shelter about 3.5 weeks ago.  She had been beaten by her previous owner and tethered outside her whole life and was very undernourished and underweight when I got her.  She's gained 7 pounds in the last 3 weeks, her coat is improving and she was spayed 11 days ago.  She has been learning very fast in her training, first learning to sit in the first week, then shake and we started working on "down" last week.  I also started working with a dog obedience trainer last week also.

She is also on Purina One, with an additive "Missing Link", to help restore her health.  And she loves the stinky chicken liver treats that I give her...or she did.

Here's the problem.  On Friday, during one of her training sessions, all of a sudden she didn't want the treats and she wouldn't "down" or sit anymore.  She totally threw up a wall and in the last couple of days will only sit to wait while I pour her food or to hook up her leash to go outside.  She is not interested in the treats if I give her a command at the same time...and these are treats that she is normally crazy about.  She walks away from them.

The obedience trainer says that she's just being stubborn, but I'm not sure.  We had off leash play time this morning, then once I put her back on leash, walked a few steps and asked her to sit, she wouldn't do it she totally ignored and blocked me out.

I'm not sure what has happened.  Could she be going through some "moodiness" from being spayed or could we have touched on some negative memory with the "down" command?  

Answer
That IS strange. It could be that she's just being stubborn and it's time to introduce some corrections for disobedience so that she understands that following a command is something she must do, and not something she can choose not to do. It could also be that now that she's getting fed every day, her food drive has diminished. What I'd normally suggest for that is withholding food, but I wouldn't recommend that in your case since your dog is not at ideal weight yet. So, I would suggest that, rather than feeding her at her regular mealtimes, use her kibble instead of the chicken liver treats during training. Essentially, what you're doing is feeding her her meals AS you train, instead of in a bowl. You might also try keeping her confined except for training times, so that the only time she gets to interact with you (and eat) is during training time. This builds drive and the bond between you.

Talk to your trainer and see what he/she thinks.

Kristen