Hi G.,
I have a daughter who started picking at her fingers (along with nail biting) when she was little - maybe only 2 years old. I tried EVERYTHING, but couldn't get her to stop.
Over the last couple of years our family has changed our diet according to the guidelines in a book called "Little Sugar Addicts" by Kathleen DesMaisons. Basically, it's about watching when your child eats, how much, getting a set amount of protein and whole grains, and eating sugar with meals. The purpose of this way of eating is to balance the child's brain chemistry.
The interesting side effect was that my daughter has stopped picking at her fingers! When I posted about it to an online forum I discovered that others had had the same result - less nail biting, less picking, fewer nervous habits.
I think the fact that it seems hereditary is a clue, as addiction to anything - alcohol, sugar, picking - is often hereditary. If her behavior keeps up it might be worth trying the simple guidelines from this book to see if they help.
Good luck!