I have pierced ears and i want another piercing i am only thirteen though. How can i convince my mom to let me

My mom is in serious oppsition to multiple piercings but i truely want this. I told her if she holds me back now then when im older i am going to rebel and get everything pierced, (plus tatoos i want a tatoo later in life). She says i am just bluffing and to move one. I know if i keep bothering her she will give in like when i got my eyebrows (mustaches over my eyes) arched or when i first got acrylic nails or when i got my first, of many cell phones. I know if i say the right thing she will be swayed, but i need help. PLEASE HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!