I'm having the same issues as this dude so I can give you the hint sentence verbatim:
Something about spying on her in her bedroom, just really turns me on.
As for your proposition, I (and Lamonster too, most probably, did all that). Normal chain of events, have her rebel, go to her work, finger her. I however didn't see the option to tell her to go commando on demand. I mean, she was w/o panties that one time, I could progress the chain of events up to fingering her, and then the game gives the "Something about spying on her in her bedroom, just really turns me on." hint, and I see no way to tell her to go to work pantyless, even though she'll work around the house without them.