I had thexact same problem with two of my daughters. I started letting them play with lipgloss or chapstick. I also brushed their lips when I brushed their teeth and we upped the intake of water. I have been a cosmetologist for 15 years and this is best. she will not get hurt if she licks her lips every time you put on the chapstick and if she also has dry skin it is definitly lack of water.
It is not 'wierd' My kids have done much wierder things, ha ha!! She is a baby in my eyes, poor thing her lips must be sore.
In university now/my kids, doing great, my son used to eat his clothes!
Especially around age 8 wait and see they all get a little compulsive. It is a phase.
This is sort of in my whole family. Our lips dry out and it is very annoying, I bite sometimes (so dont get mad at her). I agree with the above about Vaseline get her into a new habit of applying that.
One thing. does she drink enough water?
Have you tried a sticker chart? Draw a grid and give her a sticker each day she doesnt bite. this should do it + dont forget the water
she must stop doing this , and must stop liking them , because this will cause the lips to just get worse.
what i would do , is let her lips dry out , if they are terribly dry. then get a cream suitable for her age and put it on , and the lips should dry and let the old skin flake off , revealing new skin which she should leave alone , this should take around 10 - 12 days
but make sure the lips dont get to wet, because that will just make them red and possible imflamted after time