Hey, its just a little secret, what can go wrong?

So, I just got my period today, but tomorrow i'm going swimming. I'm not allowed to use tampons because my mom thinks im too young. (i'm 14) she's just crazy. Lol. So I was thinking of putting one in with out her knowing. She does not know im in my period. But, I tried asking her before and she said that I couldn't use one. So I was wondering if it was okay? I mean its just one time. Is she going to notice anything?