HELP skittish german shepherd we need help on determining if this is a new development or not, Thanks for help?

Hi, me and my hubsand recently got a blue german shepherd, she is a year old, when we went to meet her she was fantastic everything we could ever ask for she was bold confident and very friendly. ( I have grown up with GSD so i know what to look for). When we brought her home she is great with me my husband and our daughter. She is VERY smart, VERY obedient and listens to us perfectly. She is also fully houstrained and very well behaved in the house. She is pretty much the perfect dog EXCEPT for, the first night we had her home our neighbors came over and she became very skittish lowering her head and walking up to them they would reach out to pet her and she would dart from them and act skittish. This worried me.. I had a proff trainer come over and the min he walked in the door it happened again very skittish, scared and just downright scared of every move he made she wld dart. After a few mins she warmed up to him and was pretty much in his lap. Me and my husband initally got her for personal protection cuz my husband works night and i feel better with a dog in the house to alert me. She doesnt bark at the door but gets skittish. Like i said this was nothing like she acted when we met her. The trainer said it cld be cuz she is in a new enviroment.. and maybe she will come out of it a few weeks. Im hoping she does cuz she is a AWESOME dog, just wondering if anyone had any advice on what else cld be causing this ive done my research i guess i just want to know real world what ppl think.