I agree with squiggy. As long as they are safe, why does she need to be told. If she asks then you can tell her, don't feel the need to explain yourself to her.
Do you expect that she will tell you each time she gets a sitter? Do you feel you should let her know? If yes then why? So she will know your GAL? So she will ask you about it? Or so she won't be mad when she finds out?
I'm not trying to put words in your mouth just help you understand if you feel there is a need to explain things to S.
The person that you will spend the most time with in your life is yourself, so make yourself as interesting as possible.
