My parents have two female dogs. Both were rescued from the streets and arrived very young. One is already 5 years old and the youngest is about 1 year old and weighs roughly 6 lbs.
The youngest is very afraid of people, although she gets along very well with the older dog. At first we thought she was abused and she would get used to us over time, but it has been more than six months that she has been living with us and she barely sniffs the tip of my parent's toes when they aren't looking, let alone me (I don't live in my parents house but I'm there often).
Sometimes I chase her to pet her a little, but she will try to bite me and pee and poop when I catch her. I try to give her treats while she is in my hands but she refuses (she accepts if I throw it from distance).
If I touch her in the head she does nothing, but if I touch her on her back she jumps like if she was struck by a electrified wire. This makes me wonder if she has had a traumatic experience or if she has hyper-sensitivity to the touch. It is interesting the she has no problems to play with the other dog at all, they get along very well. Is there anything we can do to make her more used to us?