Reimu Hakurei could potentially be considered a Touhou girl who might write stories in some fan interpretations. She is a central and intelligent character, and it's not a stretch to imagine her jotting down her experiences in Gensokyo, which could be seen as a form of story - writing.
One possible reason could be that she was kidnapped by a criminal who wanted to keep her hidden for ransom or other malicious intentions. Another reason might be that she was being held captive by someone with a mental disorder who had an abnormal obsession with her.
No. Locking someone in a chastity belt, even in a story, is a form of extreme control and violates a person's basic rights to freedom and autonomy over their own body. It's not an ethical behavior regardless of who is doing it to whom.
I don't think it's true. Most of the time, stories like this are made up to capture people's imaginations and don't have a basis in real events. They might draw inspiration from various sources but aren't factual.
If it's Aya Shameimaru, she probably creates stories that are news - like. For example, she might write about the latest incident involving a powerful youkai disturbing the peace in Gensokyo, or the appearance of a new spell card by a certain character. Her stories would be factual and based on her observations as a journalist.
Well, it's hard to say for sure. Sometimes a Touhou comic might stick closely to certain expectations, while in other cases it could take some creative liberties and deviate.