I don't want to use the make me know everyone cheat, and this sim does not live in the neighbourhood (I've checked every house via edit town) or in another world.

Anyone got any sort of tips on finding her? We need a sim yellow pages LOL.

I've had that same problem. All I've ever been able to do is wait until I see her again. Then definitely introduce yourself.

It's been 3 sim days and she hasnt shown up at any of the places I've seen her before. I'm actually getting worried now lol. Maybe she aged up? I can't remember her name for the life of me so if she did I wont recognise her at all .

You can use twallan's mastercontroller to set the relationship (by category or numeric value) to any level for any sim. Setting it to acquaintance will simply add her to the relationship panel, if you want to work on the relationship yourself, or you can immediately set her as a friend, enemy, etc. It let's you browse through every sim in the neighborhood, which you can filter by gender, job, age, etc to find the sim you're looking for. Not remembering any of her information may be an issue, but it shows pictures and names so hopefully you'd be able to recognize her somehow. It's a lot more productive than using make me know everyone.

Do you have an opportunity that involves her, or do you want her for something else?

If this is in relation to an opportunity, it's possible she left town after you got the opportunity... in which case, you just cancel the opportunity

If the sim is the target of an opportunity and IS in town, they should have a map tag.

The opportunity system is easily broken. Feel free to drop em if they seem borked.

I "sometimes" get the "Networking Is Key" icon on the map for the target sim.

I have resolved that with testingCheatsEnabled True Mailbox Click, Make everyone known to me. If you dont want to cheat, then drop the opportunity.

Might she be a service sim? If so you could hire people until she shows up.

It wasnt an opportunity. One of my sims had a HUGE bug and I couldnt play with them anymore so I copied them to the library and deleted the original. Unfortunately that made him lose his wife to be....but I think I found her again lol.

I ended up adding (who once was) his sister and making her call the girl up. Luckily what ever the hell was wrong with the sim doesnt affect the "new" one yet so I'm good :D.