You're lucky? She's horny? How the fuck should I know? Our culture is screwed up. Women take artificial hormones that even affects their choice in mates. In some girls BC suppresses their libido, but I have heard of a few cases where it has the reverse effect.
You're still in the "honeymoon" period too, right? (been together a year or less?) We all try our darndest to wear the skin off in the beginning.
I'm not addressing why/when humans have sex, only why voyerism/pornography has always been so popular.