Do you think these are signs of prior abuse to my dog?

I got 2 miniature dachshunds 2 weeks ago. Belle is very affectionate and friendly, while Dixie is much more reserved and cautious. I noticed from the start Dixie seemed wary of my boyfriend, and seemed more partial to me, however last night my male cousin was over and he tried to pick her up and she growled and snapped at him as he reached for her. She has never growled or snapped at anyone else before, but anyone else has always let her come to them rather than going to her as her previous owners told me to do. She is excellent with my kids and likes my boyfriend, she just prefers me. Could she have been abused in her previous home? What can I do to calm her and help her overcome this? My cousin warned me to get rid of her for that and is afraid it would happen to the kids or one of the kids friends, but I don't want to lose her over a one time thing that may be fixable. Also, the 2 dogs have been together for the past 3 years since they were born, and I don't want to separate them. She has also shown what I thought were indications of abuse, when we go out for walks, if I turn my direction and my foot gets too close to her, she shys away and goes as far as the leash will let her. No one in my home has ever hit or kicked her even once, so is this probably stemming from abuse in a prior home? Additional details will be added as needed, so please check back if you ask a specific question, as I will be sure to answer you. Any and all VALID information, opinions or suggestions are welcome and greatly appreciated.