She is depressed. Poor thing. Imaging have the mentality of a two old and being moved around from home to home. She is scared, nervous and insecure.
And, you are doing exactly the right things with her. Just continue to love on her, be near her, talk to her - it is important that she hear your voice - and explore her likes and dislikes. It normally takes a week or three for new pets to settle into our home. (90% of ours are "adult" adoptions).
For the not eating - if the food you are feeding her is different from the foster home's, you may want to purchase what she is used to eating - even if it is the doggie equivalent of junk food, and then begin mixing the new food in a little at a time until the new food replaces the old.
If she is not drinking water, you may want to run her to the vets though. I also have been known to "bribe" new dogs, or sick dogs with a plain scrambled egg....don't understand it - but they love it. And, yes, my vet has said that is okay every once in a while.
Ask the foster home if she had a favorite blankie or toy at their house that you can come pick up for her (offer to replace it with a new) - sometimes a familiar object helps with the transition. We adopted an older cat who had suddenly and irrevocable lost her human and had been shuffled around for a months to various relatives. When she came to us she had a towel and a stuffed toy that were her life lines...she slept on the towel and carried the toy with her. I knew she had finally adjusted when I found the toy "abandoned" in a corner.
Your new doggie needs to get used to you, your habits, the smells and sounds in your house, oh, so many things. Be patient, give her love, and she will adjust. Animals are resilient creatures. She will come to recognize your love and understand that your home is a safe and permanent home for her.
Good Luck
God Bless