It was shown a little differently in the manga, but in the light novel, shimamura compares Pancho's and Adachi's chest size before asking if she could touch them, and when Pancho calls her "hardcore" ("are you like, big into it?") shimamura describes feeling a strange tremble running through her that she thought best to keep to herself.
Additional note! In the bath scene, she paid a lot more attention to adachi than she would admit. "So she's got curves there too, huh..." Fucking FREAK!!! Adachi seems so tame in comparison