#1.) I'll start off by asking a silly question, how sure are you that it's not a rooster?
Some women can never have a baby. Some men can never father a child. Otherwise, they can be quite healthy. A hen's internal egg making factory is pretty complicated. It's possible something is wrong to the point she will never lay an egg.
A possibility I think is more likely. I've had pullets start to lay at 16 weeks. I've had other pullets not lay their first egg until they are 9 months old or even older. I've had hens getting over the molt or pullets laying their first egg start laying in the dead of winter. I've had some wait until the longer days of spring. It's possible she was late to start. By the time she was ready to lay the days were really short so she is waiting on the longer days of spring.
If she does start she may lay great, 6 eggs a week. Or she may be one that lays only 1 or 2 eggs a week. Either is possible, it's also possible she will never lay.
Many people on this forum have this mythical mystical belief that all hens of a certain breed are identical. I see posts like that all the time on here. That's not the real world. Each one is an individual. If you have enough SLW hens most will probably follow the breed tendencies reasonably closely, but you will also have some that are way away from those tendencies on either side. Leghorns and Rhode Island Reds are supposed to never go broody, yet on rare occasions some do.
I don't know why your SLW pullet has never shown signs of laying. #2.) For all I know she may be laying and hiding a nest. Lots of things are possible. She may never lay or she may start next week. I don't know.