I can tell from the first photo that it's definitely a subadult. One more molt to go. The pectine picture is too small for me to say if it's a female or not. And I wouldn't even call it fat -- it doesn't look like it will be molting anytime soon.
As far as when to get a mate, keep in mind that she won't be able to breed until she's an adult. Even then gestation can take as long as 18 months. You could get her a male now (being sure to rearrange the tank to prevent territorial disputes) but if he's a WC adult, he may die before she's ready to mate.
Also, if you're not aware, it's easy to mistake scorpion mating for fighting. The male grasps the female's pinchers and they sort of dance around, sometimes swinging their stingers around.