oooooo this brings back memories lol, i was talking to my mum once about amrit just having a general chit chat and she was jumping to conclusions and said the exact same thing....'no boys gona marry a girl with more hair than him' ok well not exactly the same but along them lines LOL what a joke.
If kids say something to their parents which goes against their views there gona say your being disrespectful, but at the exact same time there disrespecting sikhi. tell your mum why you want to take amrit, tell her why its important, tell her why it was made, tell her about vaisakhi, tell her about guru gobind singh ji and the panj pyare, tell her about the shaheeds TELL HER HOW GREAT SIKHI IS!!!! i could go on forever but you have to make her understand is what im trying to say because when she does its going to make her think and who knows maybe guru ji will do some kirpa on her as well