Mother in law used my toothbrush?

I went to the store and bought a new toothbrush, and a pack of toothbrush holders. I hide my toothbrush on a shelf where she doesn't know where it is. That's bad that I have to hide my toothbrush in my own house because she acts like she doesn't have any home training. I also told my husband, and he said it was nasty too. I also got him a new toothbrush and case. I told him there is no point in talking to her about it, because if someone in their 50's doesn't know better than that, they will never know better. You can't teach an old dog new tricks. I left the old toothbrushes in the holder on the side of the sink, she's free to use those. I should throw those away, and see how she reacts when she sees all the toothbrushes are all gone.