The problem is that your new baby was a pack dog (with 5 Shelties) and now she's not. She doesn't know what to do as an only dog without her packmates. This will take time and patience and lots of love. It can take months, but it does improve. Just take your time with her. Sit on the floor at her level and initiate play with toys and treats she really likes. She'll get the idea.
I agree with what others have said about chicken and rice to get her started eating. The most important thing is to keep fluid in her. If she'll eat the chicken and rice, mix some warm water with it so she gets more fluid. If she won't drink water, try mixing a bit of plain chicken broth with it.
If you haven't, I would give her a crate with a blanket or bed in it too so she has a "den" she can go to. It's likely the breeder kept the dogs in crates so that's what she's used to. You can put the crate in your room so she's with you, but a crate will make her feel protected and more comfortable. During the day, you can leave the crate door open so she can go in and out of it when she wants to.
Good luck, and hang in there! Your little girl will come around.