I'm pretty sure that you are stuck with it as its more of a shading thing than facial hair.
That's pretty much it there. If you slide the sliders all the way to the left, the "shading" is lessened, and depending on skin tone and other things you've set, the upper lip/chin shadowing on the females can be almost not noticeable. However, the sliders are somewhat connected, so some other sliders, as you move them around, will swing the beard/stache sliders back to the right again a bit. So there's no single easy answer on how to create a female face with the least beard/stache shadow.
But even if you get it as good as possible, it never goes away entirely, especially under certain lighting conditions of the game. Sometimes you won't notice it, sometimes you will, that sort of thing.