I'm pretty anal about getting everything that one can get when it comes to RPGs, and apparently in this game that includes getting all the sex cards. I know there is supposed to be some villager in chapter IV that wants a sugar doll, but for the life of me I can't find her. I feel like I've talked to every woman in the village and in the inn a billion times. Any clues on where she can be found?

There's some information and a video walkthrough here

Me too, it broke my heart when *SPOILER* you had to choose between Shani and Triss in chapter three. :( */Spoiler*

Your choice in the final act also cuts off access to some sex-cards (there is one for each - order, elves or neutral). Getting all the sex cards is something you have to do on multiple playthroughs I'm afraid.

On original topic, all I can suggest is trying again. The peasant isn't obvious. I just run through the village and inn, talking to every woman. Eventually found her.

Characters often have rudimentary schedules. They'll often be standing in one place for certain hours of the day, and standing in another place (or simply vanishing) at other times. It's mostly noticeable at night (when everybody goes home) or when it's raining (and everyone clumps together in doorways) but it's entirely possible that certain characters have more complex schedules.

I had a pretty hard time finding her myself, and I seem to remember only ever seeing her in the afternoons. I could be wrong, though.

I usually find her after doing the White Honey-Sugardoll-exchange. And I never progress in the main quest until I've found her. In some of my playthroughs, she seemed to have disappeared after I went too far quest-wise. The last time I played it, I found her after doing the elven food quest, getting the she-elf-card and then the sugardoll.