Mermaid Sim Has No Face When Gender is Changed? (Edit: Fixed, read bottom comment)

It is your CC. Specifically, any skins or makeup. Whenever you have any issues always disable mods before reporting them, because they cause the issue 99% the time. Go ahead and try disabling your mods/cc real quick and see if that fixes anything.

After that you need to figure out which one it is.

I believe I saw @luthienrising post something on twitter about this issue so tagging her for you :)