One reason could be a prank. Just like in a schoolyard or a neighborhood where kids might play a not - so - nice joke on each other. Another reason could be in a mystery or crime - related scenario. Maybe he saw something he shouldn't have, like a robbery or some illegal activity, and the wrongdoers tied and gagged him to keep him quiet.
Perhaps it's part of a prank that has gone too far. Some irresponsible people might think it's funny to play such a cruel 'joke' on her without realizing the seriousness of their actions. However, this is still a very wrong and illegal behavior.
One reason could be that the robbers are just looking for easy targets. They see the girl as an easy victim, perhaps because she is alone or looks vulnerable. So they tie and gag her to quickly take her belongings without any resistance.
One reason could be that the reader has stumbled upon a secret. For example, if the story is set in a world of spies, the reader might have accidentally overheard some top - secret information and the villains want to keep him quiet.
Perhaps she has uncovered a big secret in a corporate or political conspiracy. The people behind the conspiracy don't want her to expose them, so they tie and gag her on her tiptoes to keep her silent. They may be planning to move her to a more secluded place later to deal with her more permanently, but she might be rescued by an unexpected hero who stumbles upon the situation.
In a mystery story, it could be that she knew some secret that someone didn't want her to tell. So they tied and gagged her near the stove to keep her quiet and perhaps as a form of intimidation.
In a very imaginative story, there could be a magical or supernatural element. A soccer girl might have unknowingly entered a forbidden area on the soccer field that is protected by some magical creatures. These creatures don't understand human ways and see her as a threat, so they tie her up and use a sock to gag her to keep her from making noise that might attract other humans.
Once upon a time, there was a boy who was playing a game of hide - and - seek in an old, abandoned house. Some naughty kids found him first and decided to play a prank. They tied his hands with an old rope they found there and gagged him with a handkerchief. But soon, they realized it was a bad idea and quickly untied him. The boy was a bit shaken but forgave them as they were just kids fooling around.
It could be that she has a very positive and carefree attitude. Maybe she's in a situation where she's being pranked in a harmless way, and she finds the whole prank setup so absurd that she can't help but laugh. For instance, if her friends set up a fake 'hostage' situation as a joke. She sees through the joke and just finds it really funny. Also, she might be someone who doesn't get easily frightened and can find humor in unexpected situations.
Maybe she's a hostage in a robbery gone wrong, and the key is to the locked door where the robbers have stashed their loot. If she can free herself, she can alert the police.
In a horror - themed story, it might be related to a serial killer. The killer ties and gags the girl to subdue her before carrying out his evil plans. The muffled screams add to the sense of horror and helplessness, making the situation extremely terrifying for the victim.