With the food, if it isn't her tummy, it could be what yorkies are notorious for, and that's their picky eating. She may be bored with her food. Does she respond to treats? If she won't even have treats, I'd be really concerned, but of course, you need to make sure she eats enough since she's still little. It's a good sign that she's at least taking in water.
The times you see her in that pose, do you think it might be that she's just stretching her legs a bit after having lounged around for extended periods? A lot of yorkies seem to have the habit of stretching. I would think she's still too young to have to worry about arthritis/joint pains causing her to stretch every time she gets up from resting.
I hope it's just one of the following scenerios which would be nothing to worry about (click on image to enlarge): |