So my fiancee and I adopted a sweet little 1.5yr terrier mix this past saturday from a shelter. The shelter said she had some behavioral issues and so we waited about 2-3 weeks until we brought her home. During that time we went to the shelter to visit with her and took her to some of the training classes there, and she was great! We could pet her forever, she would lay down and want her belly rubbed for as long as we were there! However, now that we've brought her home she tries to bite us when we try to pet her, and not a playful bite, but a mean bite. I'm assuming it's the change in environment, but it is very stressful and I'm scared to even put on/take off her leash because I never know if she's giving me "the look" and is going to bite me or just watching what I'm doing. She doesn't growl, just bites, which is almost worse because if she growled at least I would know to stop! She does have resource guarding issues which the shelter let us know about and gave us info on how to train her out of it, so we don't think we have anything out that she's guarding, unless she is just guarding herself. Any tips?