Another possibility is that she has some sort of stomach ailment in the context of the fanfic. Maybe she ate something bad earlier and now her stomach is protesting. Or perhaps she has a condition that causes her stomach to make noises at unexpected times, which can add an interesting plot twist to the fanfic as other characters might react to it in different ways.
One way could be to write something like 'The girl's stomach let out a low growl, like a tiny beast awakening inside her.'
Once there was a girl named Lily. She was in a very important meeting at school. All of a sudden, her stomach growled really loudly. Everyone in the room turned to look at her. She blushed bright red. It was because she had skipped breakfast that morning. She was so embarrassed but then she just decided to laugh it off and told everyone she was really hungry.
A girl may have a pale white stomach if she is constantly stressed. Stress can affect the body's hormonal balance and blood flow, which may lead to paler skin. Also, if she has a genetic predisposition to having fair skin in that area, it will be pale white. Moreover, if she recently recovered from an illness, especially one that affected her digestive system, her stomach might look paler as the body is still in the process of fully recovering and getting back to normal blood flow and pigmentation in that area.
Once upon a time, there was a girl named Lily. She was in the middle of a very important meeting. Suddenly, her stomach growled loudly. Everyone in the room stared at her. She blushed deeply and tried to come up with an excuse. She said that she had a very hungry pet mouse in her pocket, which made everyone laugh.
One reason could be that she's been really busy and hasn't had time to eat. For example, if she's a student cramming for exams all day long, she might forget to eat and her stomach would growl as a result.
Maybe she ate something bad like spoiled food or food she was allergic to.
Food is a common reason. For example, if she ate beans, which are known to cause gas, along with some spoiled food, it could lead to both stomach ache and farting. Maybe she had a meal at a roadside stall where the hygiene wasn't so good.
Maybe Naruto is just teasing Neji. In the Naruto world, friends often playfully taunt each other. Naruto might have seen Neji do something that he thought was more like what a girl would do, like being overly cautious or having a particular grace in his movements. It could also be a random joke that Naruto came up with to get a reaction out of Neji.
One scenario could be when he's in the Forbidden Forest. He's been out there for a while, perhaps on a secret mission, and he hasn't had a chance to eat. His stomach growls, and it might even attract the attention of some of the forest's creatures. It would create a tense moment as he has to deal with both the threat of being discovered and his hunger.
It could be a side effect of a magic spell or some strange potion she took. In fanfics, all kinds of magical and fictional elements can be introduced, and an improper or misfired spell might disrupt her body's normal functions, including causing diarrhea.