denying medical healthcare is abuse. a marpe and a bamp will not do anything at 18 because your sutures will most likely be closed by then. just BEG your mom into booking you an orthodontist appointment and tell her you need braces and make up problems to complain about, say you get called names at school for your teeth, tell her you have trouble chewing food, whatever idk
if she still resists then i guess threaten to kill yourself if she denies you healthcare
after you get an appointment with your orthodontist dont yap about braces. explain to him that your palate is narrow and you have trouble resting your tongue and chewing, say your teeth are crowded and you need a marpe and BAMP . if hes hesitant then i guess tell him that you have sleep apnea