My rat still seems scared of handling?

I adopted 2 rats from my local humane society a few months ago. Their names are Sunshine and Hiccup, Sunshine is 1.5 years, and Hiccup is 1. They are very very active, and not very snuggly. However Sunshine will let me pick her up without much of a fuss. Hiccup on the other hand squirms and freaks out a little whenever I pick her up. I have been trying to get her used to it, but she still seems scared of me and being picked up. I have been taking her around the house on my shoulder which she seems okay with, but if I even touch her she tries to get away. Does she just not like attention? She is a lot better than she was, and now she will take treats from me during play time or in her cage, but not when I am holding her. What else can I do to get her used to me?