Switching Insurance companies

My sister has insurance but it doesn't cover any weight loss surgery.  Can she go out and get her own insurance, how long would she have to have it before asking about approval.  Has anyone had this kind of problem.

I have been told that it is very difficult to find an individual insurance policy that covers WLS.  I'm not sure how true that is, though.  She would have to make some calls and find out, I guess.

Kelly