She knows. She's trying to let you be the one to tell her, but she knows.
No other explanation for why she'd pull down your robe but just let go once she saw the binder, and then still go "anywho, finger me. That's all I ask". She wanted to confirm her suspicions, and once she did, she backed off to the point where you were comfortable.
I suspect she wants to do more of what she saw in that guide to lesbian sex and/or be the one to do the fingering, but... she can't suggest that without revealing she knows what you're trying to hide.