Originally Posted by Merana
This is probably caused by a vitamin / mineral deficiency. I would suggest finding a good supplement for her. Another reason can be some of your girl's activities. Does she play outside a lot?
I agree with this. Mineral deficiency can lead to brittle or rough nails. Also, I would like to add that one should be careful in taking good care of the nails, especially toenails because this can lead to fungi infection.