Honestly, you don't have to tell her anything if you don't want to, you don't owe her that explanation, but if you really want to, maybe just bring it up in tidbits every so often, like references? And if she asks about it you can just tell her it's a very therapist-recomended coping mechanism and it helps you in a way? You could also just tell her to research it and figure it out that way, but I hope it goes alright if you do tell her !