How did my sim get pregnant (READ DETAILS!)?!?

I'm playing the Sims 2 for PC. My sim is eight days from being an elder...I haven't done "Try for Baby" since she had her second child, who is almost a teenager. I haven't even done regular "WooHoo" in quite a while. If it makes any difference, she has the family aspiration, but having a baby is one of her fears. No, she has never been abducted by aliens...in fact, I'm not sure if she's ever even looked through a telescope. Is she just like, the Virgin Mary or something?!