Very scared dog! How can we help her?

Me and my partner have been looking for a dog for a while and we found Susie last night.We went to see her and brought her home with us.She is a jack russell ***** 8 months old.She is Very timid and scared.We got her off a woman who was diagnosed with MS and her son decided to go at susie with a drill while the woman was out.He thought it was funny but susie was terrified! The woman said if she could shut the door on her son and never see him she would but has grandchild to think about so she advertised her.When we went the woman told us she rescued susie from a breeder.The breeder had her in a cage locked up and let slip that she wanted to "bucket" Susie as her legs were too long for breeding!! The womanrehomed her and has had her for just under a month before her son did that to her in which she hated him and he did her! When we got there she was very shy and timid although i took my time and let her come to me.The woman was happy with us rehoming her as i should have been honoured as she let me stroke her..When we got her home she was pacing from looking out the window to the back door outside.She slep on the bed with us and as soon as she was awake she was crying and pacing again.My partner has just gone to work and she has started crying worse.I have just given her a pigs ear which she is chewing and running around with.Susie is a pup which doesn't know how to play, is scared of toys and hasn't been socialized much with other dogs.What can we do to help her and build her trust.? Sorry its been soo much. Just to let you know she is eating and doing her business fine.