skiddish

we have a new addition in our home...she has been w us approx 3 months..her name is MiMi...she is a wonderful dog..but seems to be afraid of EVERYTHING>>>at first we thought it was cause she was in a new place w new people..but she doesnt seem to be coming out of it...any suggestions? she wont walk on the leash out of sight of the house...you walk towards her and she cowers down...sometimes peeing...she is 4.5 yo...could she have been abused before and we werent told?? There hasnt been any aggression...just worried and want her to feel secure.