Period advice urgently!!!!?

My daughter has recently started her periods and (she's 12 btw) now she has to wear summre dresses with knee high socks. The boy in her class aren't particually nice and if they get to know will make fun of her a lot. So her summer dress finishes litterally right above her knee but she's worried that when she sits down or something like that somebody wll see the pad on her knickers. Her periods r very light so thats gd and her knickers r white but she's still worried.