Sim born with assymmetrical face

So two of my CAS-created sims with perfectly symmetrical faces, who already had two children beforehand with no remarkable facial features, recently had a third child, and this is what she looks like after aging up:

https://abload.de/img/assymetrischesgesichtmdksn.jpg

This... anomaly or whatever, that keeps her mouth perpetually half-open on one side is caused by a mod, as I discovered upon restarting the game with no mods and finding that it was gone. No idea why, I suspected a fancy skin detail, but she doesn't have any. Must have something to do with the cheeks, because choosing different cheeks (any of the presets) removes the anomaly, choosing a different mouth doesn't.

But now I'm debating whether or not I should even fix it, or keep it like this. Real human faces aren't symmetrical either, and for the game this is quite unique. I've never seen anything like it before, and it's only really noticeable when you look at her up close in CAS. What do you think?