She was basically confirming whether the rumors about his sister were true or not. She purposefully baited her to see if she would give a "slutty" answer but subverted expectations by showing she's a pure gal with no experience. That's why she immediately "gives up" and leaves once she confirms she's a virgin.
She's purposefully teasing and flirting with Tanuki to get the other people who were just previously spreading rumors and speculating on Tanuki's relationship to the "slut cheeky gal from the other school" to focus on there apparent relationship instead. Tanuki seems to understand this which is why he sort of played along but he's still not comfortable with her getting handsy with him.
I still stand by my previous prediction, I foresee Mochizuki helping Komaru by the end of this arc in some way and ingratiating herself to her and becoming her friend. The introduction of the creepy teacher again just reaffirms my speculation, he'll try something and Mochizuki will run interference.
