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 说 she'd think about it , then the 下一个 日 she 说 "No, I don't' want to trade some thing that 你 should be doing for some thing I don't want 你 to be doing." I even looked up non-toxic, non-smelly nail polish! I need some 更多 REALLY GOOD reasons, please. Thank 你 all in advance.