Child Behavior: Nail Biting
As a general guideline, the best advice would be to realize first that you, as the parent, cannot control the behavior. Your child is the only one who can. Do not punish or criticize your child for the behavior, and do not constantly watch her to try to catch her at it. Instead, keep your child's nails trimmed short and filed smooth at all times. If any sharp edges appear, trim and file them immediately. Sometimes polishing your child's nails can be an incentive for her not to bite and damage them.
If you can identify the times, places and activities most associated with the biting, you can perhaps help deter the behavior by having her wear white cotton dermatological gloves, or else put tape or adhesive bandages over the nails in question. For some nail-biters, the use of sugarless gum or mints can provide the oral stimulation they are seeking in a nondestructive way.
Finally, to motivate your daughter to work on the problem on her own, help her chart her nail biting on a daily basis to make her more aware of her own behavior. You can also use this chart to set up a system of small rewards she can earn on a weekly basis for good performance.
If the problem persists despite everyone's best efforts, or if your daughter is causing herself a lot of physical damage, it would be advisable to see a behavioral therapist with some expertise in this area.