How can one sim get another pregnant and never have met?

@LSM36 You can also summon any Sim by name to your lot, so if you are trying to find someone, rather than searching all the worlds for her, you can go the mailbox. It's under household cheats, right at the top, Summon Sim. You have to type their full name and they will come to your lot. Also, the search sims info mod is a gamechanger. You can use it to look up so much about any Sim you want, their relationships, traits, location etc.