Sorry this has happened. I was on holiday with some people and one of them posted photos to Facebook, the other people asked her to take them down. You could ask your grandaughter to help you with Facebook next time she comes round, and make notes when she shows you so you can refer to them and do things with confidence.
My aunt is 83 and hates tech, but joined Facebook. Even though I've told her, she still doesn't realise her comments are world public when she writes on someone's page - unfortunately I'm too far away to help her. My daughter's boyfriend produced a film, Roy, about a lonely man phoning people at random from the phone book, it was chosen for the Santa Fe film fest - my aunt commented that she felt the same as him, just waiting for the phone to ring. My daughter messaged me to say she knew I phoned her all the time! 