Taking from my own experiences again, I would suggest for a 10-12 year old girl you could get some earrings and she'd like that.
I don't know how an unpierced girl would welcome clip ons, in my family we were allowed to pierce our ears at 8, so I was over clip ons by this age. But if it's your only option it might work? If you don't think so go for a jewelry set, but that's getting a bit more pricy.
I forgot to mention that some of these gifts would work for other age groups. Like this one: joke products.