I know that many puppies have a of biting their feet but this isn't that simple.

We've had our rescue staff cross jack russell since she was 6 weeks old and she's now well over 2 years old. She never bit her feet as a pup but recently has started biting her nails! We've checked that it's not her feet, there's now fur knotted in between her toes or anything like that..... In fact her claws stick well out as is typical for the breed.

It's very confusing, does anyone know of a reason this might be? Or is it just a weird habit with no significance?