She's still young, shouldn't be too big a deal.
I agree with Michelle~a "bite" is ill intended and/or breaks the skin.
A soft, quick muzzle touch MAYBE with one or two fingers, if done properly, can be effective, but can also backfire and tick some dogs off that weren't ticked to begin with. I'm not a fan of the whole making them bite their own tongue bit, either.
A schrill "uh!!" will usually do the trick. Occasionally you will get a dog that gets more fired up that way and mouths more, but not usually. In that case, removing your hand and ignoring usually works well.
Dogs that have been taken from their moms too young or that have been bounced around often do not have good bite inhibition, so I agree with "jlewin," also. This is a good time to teach her "soft mouth," or how to "go easy."
I have one who was Mr. Mouth, so rather than making it a constant issue, I did what Marinepits did---I taught him to "get a toy." He can't stand to greet anyone now without a toy in his mouth, and he was prone to a 'naughty mouth' before that.