I'm a fan of the Sims franchise--moreso the Sims than Sim City--but my girlfriend LOVES the series. I can related in that it's drastically different compared to the usual impossible guy having impossible adventures, sci-fi laser gun battles, military/black ops bullet battles, sneak attacks, headshots, swords and arrows dragon slaying, anime artwork, grim dark, zombie storyline, zoom I have a car-games.
I get why my girlfriend likes the sims as well since the majority of games tend to be male centric and even when playing with a female character there's rarely strong female leads written well--plus sometimes the stories just wouldn't entertain her, but that's true for everyone. The Sims is a game without static stories, heavy canon, and it has that use your imagination ethic and make your own stories that was present in early gaming. While there are aspirations and stuff, you make your own end game. There's no game climax or anything and there's no needing to play the last game to get the next's story.
I also like seeing her play the sims. She still has this several year old game of the Sims 2 saved. Multiple generations. She's into Sims 3 at the moment, though.