"Leah, mess yourself pretty please." Tina brimmed with excitement at how much control she had now, making Leah into a little potty pants. She can push the line a little further. Besides, they were alone, and Leah had proper protection this time.
The teen looked perturbed, shifting around in her seat in discomfort before leaning forward and scrunching her face. Tina could see in the rearview mirror when the girl knew what was happening but was powerless to stop.
"Are you alright, Leah?" Tina asking in mock concern.
"Y-Yeah." She responded in a strained voice, trying an failing to act inconspicuous---a little difficult when you're trying to poop your pants. She kept shifting around, trying to find a good position to poop while also trying to stop, little quiet grunts coming from her. A tiny toot comes from the back, and Leah's face flushes red. It turns brighter when she grunts and let's out an audible fart.
"Goodness, Leah, excuse you!" Tina teased, getting a groan of embarrassment from the girl. She stops shifting and leans her whole body forward, hands on her knees as she scrunches her face, and a much louder fart putters through the car, followed by squelching. The bowel movement began proper, the smell alone giving it away. Leah then continues to push, face contorted in effort, confusion, and embarrassment as several nasty farts blast out, followed no doubt by quite a bit of poop. After about 10 minutes of pooping and farting, Leah let out an involuntary sigh of relief, sitting down with a splat and a cringe.
"Are you done?" Tina askes, not even bothering to pretend she didn't know what was happening.
"Y-yeah." Leah said tearfully, "I...don't know what happened."
"Clearly you needed to go, Leah."
"Yeah, but, I..." She paused, probably not sure how to say 'I purposely pooped myself, but couldn't stop' without sounding silly.
"This just proves my point. You need a little potty training."
Leah says nothing, just grumbles as she tries to find a comfortable position in her dirty training pants. If there was ever any doubts about her needing potty training, they've now been thoroughly dashed.
As they got home, Leah exited the car with uncertainty, trying to hide her loaded pants from any neighbors.
"Come on now, in the house." Tina said, forcing the teen to exit her hiding place. She power walked into the house, making Tina chuckle. Honestly, this side of Leah was incredibly cute. She almost wants to take it further. Tina frowned at the thought. She's already pushing ethical boundaries as is. Should she quit while she's ahead, or double down?