Does a trait for sickle cell show up later in life rather than sooner?

[No R]

I have a friend who has been sick for so long and has gotten progressively worse. Joints have been hardening up and everything like that. I have been just as worried as she was, so it felt good to know that she went to the doc. The doc blood results showed that she has a sickle cell trait which I am worried about. She was supposed to have known that since birth, but the blood test just showed this info today. What I want to know is- could it be more serious than just a trait? Would the blood test have shown if she had the actual disease? WHAT disease could be causing joints to harden and freeze??