The person you need to talk to is the bartender, she will contact you when he comes in after you've spoken to her (not sure if you have to get a certain amount through her questline first though). Mia's footage has nothing to do with lust you are missing something there, my hint is you can go into her room in the mornings when she's in the kitchen/bathroom.
I've never met the bartender, I assume? And I've talked to everyone possible, to no avail. Mia's lust does have to with her own storyline/quest, at least that's what the game tells me. And I have invaded her privacy. I setup the cam. Checked out the bookshelf with cat magazines, the desk that's very clean and tidy and sniffed her panties, "borrowed" them, dirtied them and even returned them twice now... I've maxed her affection, at least through conversation at this point, do I need to max out her submission up this point in the story?
The spycam is all you need for that quest, Mia will at some point do something and then you have a prompt to record it.
Bartender is what you need to continue sages quest, do some main quests. I'm guessing you haven't been inside the bar yet? After you do some side quests your partner will ask you if you want to go out and drink and thats how you meet the bartender. So maybe go check at your office and see if he will invite you out.