I applied a bleach to my DD's upper lip from about age 9 it was all it took for it to virtually disappear. It took 5 mins once a week or so. She is Anglo with only a light tan so it worked well. Sometimes though we would mix it too strong and it would sting a bit but she was fairly resilient LOL she does it herself now (she's 15yo). She has also always gone to girls' only schools and i found the teasing less than what I experienced when i was at school.

If your DD has dark skin though bleaching might not look right... maybe do a Nair patch test somewhere less sensitive like on her arm to see how that goes? I don't think 8 is too young if she is being teased.