Your daughter seems to be having PICA.
PICA is a syndrome that usually occurs in kids as a behavioral problem. It's characterized by eating sand or nail biting etc. But, it is known to occur in adults also. I consider you test your daughter if she is suffering from iron deficiency anemia. Usually those who develop PICA are anemic in specific iron deficiency anemia. There is nothing you have got to worry about.
Start with clipping off her nails weekly, so that she has nothing to bite. And go for a blood test; check for her hemoglobin levels and also in specific check for iron levels and transthyretin levels.