It could be that the girl was under a spell or curse and biting the frog was the only way to break it. Another possibility is that she was extremely curious and wanted to see what would happen if she did it.
Maybe she was dared to do it. Or perhaps she thought the frog had some special power and biting it would bring good luck.
I have no idea off the top of my head. It's quite a unique event, and it might be from a lesser-known or newly published novel. You could try searching online or in specific genre sections of libraries or bookstores.
One possible moral is that we should respect all beings, no matter how they look. The hot girl might have looked down on someone who turned out to be more powerful, and her transformation into a frog is a consequence of her lack of respect. Also, it could teach us about the importance of inner beauty. When she was a hot girl, she might have relied too much on her looks, but as a frog, she has to find other qualities within herself to be content.
Well, both girls are likely to be in touch with nature more. The girl without a phone might spend her time outdoors, just like the girl in the Princess and the Frog story who probably had a connection with the natural world around her swamp. Also, they both might have a sense of adventure. The girl in the story had the adventure of turning the frog into a prince, and the girl without a phone could have adventures in her own environment without the distraction of a phone.
The moral could also be about the value of different perspectives. The girl comes from a world with phones and technology, but the frog princess from a more magical and traditional world. By interacting, they both learn from each other. It shows that we should be open to different ways of life and thinking, even if they seem strange at first.
Poor hygiene. If the girl doesn't wash her socks regularly, they will start to smell.
Perhaps the girl, without the distraction of a phone, ventures into a forest. There, she meets a frog who is actually a cursed prince. Since she doesn't have her phone to distract her, she notices the frog's unique charm and decides to help it. Through her kindness and lack of modern distractions, she breaks the curse and they live happily ever after.
Maybe it's for a performance like in a school play or a local theater production. It gives the boy a chance to step out of his normal role and try something different.
In some stories, it could be for a play or a skit. The family might be putting on a show at home, and the brother was given the role that required him to wear a girl dress and diaper. It could also be that the family was just having a really silly and creative day, and dressing him up like that was part of the fun. It's all about family bonding and having a good laugh together.
Maybe she's running away from a bad situation at home or trying to escape some sort of danger.
If the 'TF' story has a certain theme, say a magical world, the Frog Girl could have magical powers related to water or nature, as frogs are often associated with those elements. Maybe she can communicate with other amphibians and use that to her advantage in the story. She might also have a unique appearance, like having frog - like eyes that can see in the dark or webbed hands and feet that help her in her adventures.