How To Grow Thicker Hair?

My daughter had Trichotillomania and we were using rogaine to help her hair to grow in quicker, then we stopped using it and it got thinner and it seems like it has stopped growing. Is there anything we can use to help it grow in quicker? We don't want to use Rogaine again because if we stop using it, it will get thin again. She has not pulled her hair in a year and a half and its still only grown a half an inch. Please help if you have any suggestions.