Hi Fein!
I have worked with my share of fearful, anxious, abused, confused, and insecure dogs. Your new dog may simply not be as receptive to the use of treats or any specific type of training, yet. But, this will change with time. However the use of treats will be of benifit when you want her to associate "good stuff" in certain situations.
I usually just try to get the dog to feel secure, safe, and know where their place is within their new family or "pack", before I do anything else. Just not putting any additional stress on her right now while she is in this fearful state, will help. If she is not receptive to you offering her a treat just yet, give her a little time to adjust and feel more comfortable.
I can get more specific on what to do here, but will wait until you get some other viewpoints on what might help.
The good news is, many dogs I've worked with who are fearful, are also very smart and easy to communicate with, once they start coming around.
