Its a security thing. It even sounds like a security thing. I used to suck on my lips, because I used to suck on my fingers or chew my nails and I got into trouble for it. Sucking on my lips was an emotional behavior for me. It soothed me when I was either nervous or scared. Can something be troubling her? Ask?! She will eventually grow out of it. My neice sucks on her fingers and my sister has tried everything to stop her from doing it. She is 12 years old and I know once everything smooths over for her and right, she will stop. There could be some issues with the dad or even seperation issues. I know my parents were almost always gone, work, bars, just away from us kids and I got insecure for the longest time. I always felt that I needed my mom. You can talk to a doctor about what you can do. But I don't think he can help much other than telling you to take her to see a psychologist. I know its hard at times to say, "I don't think there's anything wrong with my child/I don't see much of a change in her." But when I talk to my neice, she seems to release a lot of tension and issues that soon go away and I notice that the less she sucks on her fingers. I know that some kids go through some stuff that us adults don't see or hear about. School is another issue. Some kids don't talk about it, because they are ashamed and they don't want to feel like a tattle taler so some things they don't see that its a BIG DEAL. But really it is. My middle child goes through this thing where she loves school and has a lot of friends, yet some times girls can be cruel and harsh and some times certain friends say and do some mean things to her, she'll tell me school was fine, until my older daughter gets home than they start arguing and fighting. Than my middle child will yell out that she had a horrible day and she feels like no one likes her. It breaks my heart and I will ask her again what happened at school to make her react like that. She than will tell me about the certain friends that hurt her feelings. Or the teachers who made her feel so dumb. It'll work itself out sooner or later. Good Luck!