How can i convince my mom?

Okay, so i was talking about getting my eyebrow pierced to my mom and she seemed for it but she was like oh youll have to convince your step dad tho, which i guess she didnt think i could do because he is super strict . But what do you know i did and he said it was fine and everything, but as soon as he said it was okaay all of a sudden my mom was completley against it and we got in this huge conversation or at least an hour about it and i did all the research on it where you can get it done how much and will it leave a scar? She knows i can take care of a piercing cause ive had my earpierced twice (i know its not the same but still) She thinks that 14 is 'too young' to get a piercing on your face and maaaybe little chance i can get it done at the end of summer even tho im paying for the hole thing myself.Please no negative comments on how i am too young . Can anyone pleaase help and tell me how i can convince her.