Another possibility is that it's part of a role - playing or a game in a more innocent context. For instance, in a pretend play scenario where she is imitating a baby for fun with her siblings or friends.
Maybe she has some medical issues like incontinence. For example, a urinary tract infection could cause problems with bladder control.
It could also be due to psychological stress. Sometimes, when a girl is under a great deal of stress, she might regress in her behavior, including something as basic as toilet training. In the story, perhaps she has just gone through a major life change such as moving to a new place or starting at a new school.
Look to Chapter 60 for the clearest answer. It begins with What's with Jiang Yan, treating his own sister Jiang Li like this?" "He..., keeps building through When Jiang Li found a place to live, she didn't bother with him either,..., and lands on And in traditional characters?" "What else?.
The best chapter pointer here is Chapter 42, "First Impression Score". It opens with You've all met now, so this game is very simple," Director Sun said. and closes on As the plane hadn't taken off yet, and the live camera was still running,....
A practical answer is Chapter 34, because it turns the idea into a concrete scene. The chapter opens with Seeing that the public sentiment wasn't quite right, Su Yinwan felt..., adds pressure through Hurry up and start the live show, I can't wait to watch the universe's..., and ends on Now that.
The best chapter pointer here is Chapter 41, "Actually Still the Museum Director?!". It opens with The live streaming room suddenly boiled over again. and closes on In contrast, Wen Jiaojiao didn't have such awareness..
Look to Chapter 42 for the clearest answer. It begins with You've all met now, so this game is very simple," Director Sun said., keeps building through That is, give each of the other five people in the room a score based on..., and lands on As the plane hadn't taken off yet, and the live camera.
Chapter 46 is the strongest chapter-level answer because it starts from Upon hearing this, everyone but Jiang Li perked up with high alert. and follows through on Did you calculate the score incorrectly?!" And 13 points?!.
The best chapter pointer here is Chapter 21, "Uncle Policeman, They Are the Ones Causing Trouble!". It opens with Jiang Li's clear and logical explanation had everyone stunned in place. and closes on But the implications could be different..
If you want the clearest chapter reference, go to Chapter 57. Early on, Lu Xingchao's numerous fans were stunned.; later, the chapter leans on Holy shit, what's up with God L?.
The best chapter pointer here is Chapter 68, "She finally managed to win a round back!". It opens with Jiang Li carried the noodles straight out of the kitchen and came to the... and closes on But didn't Uncle Zhao say he was still sick?.
The best chapter pointer here is Chapter 63, "Far Exceeded Expectations!". It opens with During those seven days, he thought he had completely escaped from that... and closes on It was already past midnight, but the conference room at Xingmei....