One plot could be a nanny being hired by the Weasley family. The nanny could be a muggle - born witch who brings a fresh perspective to the chaotic Weasley household. She might help Ginny with her magic studies while also trying to keep the twins from causing too much mischief around the Burrow.
Another option is Wattpad. Although it has a wide range of content, there are some good 'Harry Potter' fanfictions. Search for 'Harry Potter wanted' and browse through the results. However, be aware that the quality can vary more on Wattpad compared to the other two platforms.
One great 'Harry Potter wanted' fanfiction could be one where Harry discovers a hidden power within himself earlier. For example, a story where he realizes he can communicate with magical creatures in a more profound way from a young age. This changes the whole dynamic of his Hogwarts experience as he's able to get help and advice from the creatures around the school grounds.
It could be that the characterizations weren't right. If the characters act out of character, it can disappoint fans. Also, the writing style or the pacing might not have been appealing.
First, know the source material well. Read the books and watch the movies multiple times to understand the characters, the magic system, and the overall world. Then, come up with an original idea. It could be a new adventure for the characters or a different take on an existing event.
You can find Harry Potter fanfiction on websites like Fanfiction.net. It has a vast collection of stories written by fans from all over the world. Just search for 'Harry Potter' in the search bar, and you'll get a long list of fics to choose from.
It could be about a character's deepest desires within the Harry Potter universe. Maybe it's about a wizard or witch who has always wanted something like mastering a powerful spell, finding true love at Hogwarts, or perhaps getting accepted into a secret society in the wizarding world.
She might give him harsher punishments than other students for the same offenses. For instance, if Harry is late to class, she could give him detention while letting others off with a warning.
One sign could be that his partner constantly criticizes him, like always finding fault with what he wears or says. Another might be that his partner tries to isolate him from his friends. For example, making excuses for him not to go out with them.
The nanny should definitely be good at magic. Since it's the Harry Potter world, she needs to be able to protect the children from magical threats. For example, she should be able to cast strong defensive spells.