It could be Ginny. Since they got married in the original series, it would be a natural choice for Ginny to be the mother.
Well, in some fanfics, the mother could be a new character. Maybe an American witch who met Harry during one of his international wizarding trips. She could bring a different perspective and culture into the family. But if we stick to the main series' lore, Ginny is the most likely candidate as she was Harry's love interest and they ended up together.
Obviously, Harry and Ginny would be main characters as the baby's parents. Their friends like Ron and Hermione would also play important roles. Ron could be the fun - loving uncle figure, always making the baby laugh with his silly jokes. Hermione would be the knowledgeable aunt, perhaps helping with the baby's magical education as it grows up.
Her magical education would likely be different as she might have an innate understanding of dark creatures due to her connection to Cerberus. For example, in Defense Against the Dark Arts, she could already know a lot about hellhounds and other similar creatures without having to study much.
It could be some of the pure - blood supremacists. They might see her as an abomination because of her connection to Hecate, who is not part of the traditional wizarding families. They would try to undermine her at every turn and make her life difficult at Hogwarts.
It could be an original character created specifically for the fanfiction. Maybe a mysterious woman Jaune met during one of his adventures who he had a brief relationship with.
The mother could also be a completely new character created specifically for this fanfiction. She might be from a different realm or have some special powers. And her relationship with Percy could be a complex one, filled with secrets and misunderstandings that led to the situation of having a secret daughter.
The fanfic could also be about how Harry's past experiences shape his parenting. Given his own difficult childhood, he would be extremely determined to give his baby a loving and secure environment. He might teach the baby about the importance of friendship and courage from a very young age, and the baby could grow up with a strong sense of justice, much like Harry did.
She can submit her Harry Potter fanfic on various platforms. Fanfiction.net is a well - known option. It has a straightforward submission process. You create an account, then you can post your story in the appropriate category, which in this case would be Harry Potter. AO3 is another great place. It's known for its inclusive and organized approach to fanfiction. It has a tagging system that helps readers find your Harry Potter fanfic easily. Wattpad can also be considered, especially if she wants to reach a younger and more diverse audience.
It could be a new dark wizard who is jealous of Harry Potter's fame and success. This dark wizard targets Harry's child, thinking that by causing trouble for the child, they can somehow diminish Harry's reputation in the wizarding world. He might try to frame the child for various dark magic incidents around Hogwarts.
The daughter herself is often a great character in these fanfics. She usually has a mix of Harry's courage and some new traits of her own. Her friends can also be really interesting characters, like the ones who might come from different magical backgrounds and bring diverse perspectives.
Well, it could be about her discovering her powers. Maybe she has a natural affinity for magic related to Hecate, like powerful divination skills. She could struggle to fit in at Hogwarts as her powers are a bit different from the norm. And she might face some challenges from those who are suspicious of her because of her unique heritage.