Dianne, some of them are just different. Very wary, or very timid, sometimes there isn't an obvious reason (like former neglet and mistreatment) for them to be like that.
It's so frustrating and sad, sometimes.
In many months with my Sesamo I only managed to teach her to go to bed without towelling her.
In the morning when we all have a bit of toast together I can see her burning with the desire of coming to me and get her share of crumbs. Sometimes she flies to my lap and then she gets scared by her own temerity and runs away yelling.
Emma seems a lot more willing to get close to you, just give her time and she will learn to trust you, I am sure of it!

Thank you Barbara, for the encouragement.