Why does my mum do this?

I'm in the middle of trying to use tampons. I hate talking about my period when my dad or sister is around i know my sister is going through the same thing but i'm very sensitive about my periods. I've told my mum loads of times to stop asking me about my period in front of my sister and dad but she still does it! Today i came from a shower and she asked right out loud infront of my sister did you try a tampon and when i said i don't want to talk about it she gave me a dirty look. How do i stop her from doing this i've told her so many times now!