How do i tell my mom i wanna start shaving?

im 11, and we just had the puberty talk. afterwards my mom asked me if i had any questions. you can tell she felt VERY uncompertable with it. it almost seems like shes upset and nervous with me growin up. i know she is but its ten times worse than most moms. well anyway, i need to start shaving my armpits cuz in one week for spring break im goin to virginia beach. ill be wearing a swimsuit a lot and im not walkimg around with exposed pits. i dont really want to go behind her back cuz she my mom and shes tryin and i want her to be part of my life. anyway my moms not goin to virginia beach so i have to do it befire. please please help!!!!!!!!!!!!!