You need to stop her otherwise she’ll have very dirty lips; I mean cracked and chapped. I don’t know how you’ll do that but you need to. You can start by listing her all the possible disadvantages of her act. I think this is going to be enough to awaken her.

If she has such a nasty behavior then she should quit wearing lipstick. This will be a lesson for her. At seeing her dull lips she understands her wrong doing and I’m sure she’ll do her to control her habit. So, explain to her that she should quit the idea of wearing lipstick.

Let her.
She doesn’t do that on purpose, this is something that happens naturally and there are no ways to stop her from doing that. This habit of hers can only be cured with time. One day the habit will go.

I have an excellent idea to restrain her from chewing her lip. What you need to do is to keep her entertained. Ask her to chew a chewing gum to keep her entertained. Isn’t it a nice idea?

Even lipstick are nutritious these days so let her eat her lipstick. Why are you bothering about your friend when she is not the least concerned about her? Let her on her own she’ll realize her mistakes. Stop treating her like a child.

She chews her lips; she must know what she is doing. Your friend is not a kid that you need to watch her. She has to react and not you. Leave on her own stop treating like a baby. I know she is your friend but let her solve it by herself.