How to convence parents to let me get tongue pierced?

i'm 15 years old and i want to pierce my tongue. i'm really afraid to ask because she might yell at me like the time i got my cartilage pierced. i also have a navel piercing that she agreed to. my mom had hers pierced and it got infected, now she is against them. how can i ask? PLEASE HELP ME!! i also know a pro piercer at Planet Ink.