Should I worry about my 2 yr old pulling her hair out as she lays down for her nap? Bald spot forming in back. Spoke to ped didn't seem concerned

Trichotillomania. Trichotillomania is no more worrisome, imo, than any other bad habit, except that others can see the evidence. The hair will grow back, but you want to gently break this habit before it gets entrenched. You might consider cutting her hair short enough that she can't pull it, or braiding it (not too tightly). And perhaps get her a stuffed animal that she can pull at instead, as a distraction.
Worth watching. You don't indicate how long this has gone on and if something has changed in the child's life. Hair twirling often is a self-soothing behavior that may indicate the child is feeling under some type of stress. It well may pass on its own. If it does not, consider meeting with a young-child mental health specialist to discuss possible causes.