My daughter loved going to the nail store (every store was named after what it sold or did. Yes, Starbucks is still the coffee store and she's 7.) with me. Occasionally, I'd like her get a light pink or clear coat. I told her we couldn't get her nails done if she bit them.
I noticed she had gone several days, with helpful reminders (I put NAIL STORE on the calendar and reminded her often when we were going.), then I took her to get hers painted. The kicker was, I let her pick a different color (It had to be light and I think it was dusty blue.), but reminded her that she shouldn't bite the nails. The gals in the salon also talked about how important it was not to bite the nails. They explained how it hurts the nail bed, infection, etc. She's a smart kid and I think the explanation was what did it...and wearing blue nail polish.
That's what I did.
S