Any way to convince my mom about my braces....?

Ok so i've had braces for about 15 months now. I'm 13 and my sister is getting married June 27. I was supposed to be able to get my braces off before her wedding, and my mom even paid off the remaining balance of the braces so i could be done with them when we needed to be. but last MOnday, i had an ortho appointment and the lady basically said there was no way in hel i would be getting them off before then. she said she wouldnt because there is a tiny gap, maybe 3 mm across, on two f my theeth. AND, its in the back so its not like you can see it. i dont care abouot the gap... but thts why she wont take them off. and now she's saying october. my mom got mad and wont talk to me or my ortho lady about it. so what can i say to her? ive given her time to think and havnt said anything about it, so its not like ive been bugging her about it. i havnt said anything. and it hurts to eat STILL and i get headaches and i just want them off. my teeth are fixed, but she still says i cant have them off. (my ortho, not my mom) so what can i say to my mom, so she wont just giv up and let my ortho control her. my mom is kind of a weak person, and the ortho is very like, 'forceful' and she kinda scared my mom into playing along last time. so is there anything i could say/do to get my mom to understand my position, and keep her promise?