I need help FAST!

Hi, I'm trying to convince my mom to let me buy nail polish again. She hates when I wear pants so I told her I would wear medium skirts for a whole year. She said she'd think about it , then the next day she said "No, I don't' want to trade some thing that you should be doing for some thing I don't want you to be doing." I even looked up non-toxic, non-smelly nail polish! I need some more REALLY GOOD reasons, please. Thank you all in advance.