Ignore it. The more you call attention to it or try to get her to stop, the more shame and anxiety it causes (even if you do it nicely). Keep her occupied. You can redirect her attention by giving her things to do with her hands. This will keep her from doing it without making it an issue. Ask her if she wants to color or play with playdoh or play catch or have a snack or a drink or give her some fidget toys (squishy balls to squeeze, etc). As a part of her grooming routine, clip and file her nails to keep them well groomed. Ragged nails encourage more biting and chewing.