M.P.
I agree with Melissa. Biting nails can be a power struggle as well as a sign of anxiety. I, too, recommend that you pay as little attention as possible to it.
However, I would still try preventative measures without scolding the nail biting. Have you tried trimming her nails every day. You can "use" the clippers even when the nail isn't really long enough to clip. Keep her nails clipped short enough that it's difficult for her to catch it with her teeth.
And painting all of the nails might work since it worked on the thumb.
I'd find some other way for her to deal with her anxiety or "nervous" energy. I visited Greece and saw lots of "worry beads." I was told that the people played with the beads when they were walking, talking, or doing anything that didn't use their hands. The ones I bought were a bracelet of beads strung on cowhide and tied at the ends with a slip knot so that you could also swing a short tail of beads or tighten and losen the bracelet.
My grandson has several small bouncy balls that he bounces around when it appears that he's getting antsy. This keeps him up and moving.
Does she chew her nails while watching TV? Perhaps you could introduce some other hand activity while she's watching. My 9yo granddaughter, until the last few years, rarely just sat and did anything. She danced to the music, did summersaults, talked along with and in general kept busy so that she didn't have time to chew nails.
She did go thru a short stage during which she chewed her nails every day but not down to the quick. She still "trims" her nails by chewing on them if she doesn't have any clippers. Still it's not down to the quick. She just likes her nails short. My idea would be to have a nail grooming time with your daughter. "This is how big girls take care of their nails. Some like them short, some long. Nail polish really makes them pretty." Again don't tell her to not bite her nails. Just tell her how to make her nails pretty now that she's a big girl.