THICCER, like 1.5x to 2x bigger legs/thighs/butt.
Big breasts. As big as her head is overdoing it, but also not discouraged.
Tapered, but not thin waist. It should be a little soft.
If she's black like some have suggested, give her kinky hair. That's not really THICC-related, I think think black chicks look really cute with it.
Bike shorts? Or maybe leggings? Or maybe leggings under shorts?