Karen seems like the type who'd attempt to pee standing up, using her fingers to make the pee go forwards. Once she feels that she has gotten good enough, she'd then promptly drop her pants in front of Koyomi and show him how she can pee on the side of the house. It probably wouldn't work and her brother would just give her a slap on the butt and walk off, while she sits there with wet pants around her ankles.