basically what the title says. approach her by commenting on something about her eating her nails.i dont want to be roud but i could say something that might sound roud but with confidence and a smile it wouldnt matter i think..

so any tips on what i could say

ask her what flavor they are and where can you get some.

I like the idea about asking the flavor of the nails, that seems like a good one.
But you don't know, some people are actually self conscious about nail chewing/eating. I used to do it heaps until I stopped and hated it when people point out that I chew my nails. It becomes like a habit, it's not something you can stop easily.
So opening to a girl about her chewing her nails may not be the best idea.
Try to open with something else (not about nail chewing), and once you've built comfort you can tease her about it then and maybe incorporate it as a neg, so once you get her attracted to you then you can say what flavor are the nails, she will find it funny because she will know you mean no harm.
Whereas actually pointing out to a girl that she chews her nails could make you look bad...chewing nails is not the best of habits, especially one not to point out to someone whom you don't know, even if it's in a lighthearted way...

true, thanks mate