Sam and Dean Winchester are likely allies. In the Supernatural world, they have a history of helping those in need, especially when it comes to the offspring of supernatural beings. They would probably see her as someone to protect and guide, given their own experiences with angels.
Hermione could be an ally. Hermione is known for her intelligence and open - mindedness. She might see the potential in Bellatrix's daughter to change and be a force for good. She could help the daughter learn about the positive aspects of magic and the wizarding world.
The Teen Titans could be potential allies. They are known for giving second chances and helping those who want to turn their lives around. If Deathstroke's daughter shows that she wants to be different from her father, they might take her in and help her develop her powers for good.
There's also a possibility that some of the more morally grey characters in Gotham, like Catwoman, could be Bella's allies. Catwoman has her own code of ethics, and she might relate to Bella's struggle between good and evil. They could work together in certain situations, especially if there are mutual benefits involved.
Another storyline could involve her trying to find out more about her father, Gabriel. Since he was a rather mysterious character in Supernatural. She might go on a journey to discover the secrets he left behind, and in the process, encounter some of the other well - known characters from the show like Sam and Dean. They could initially be suspicious of her but then come to accept and help her.
There's also a possibility of her allying with some of the more neutral houses. Houses that were tired of the constant fighting between the big players. Her daughter could offer them stability and protection in exchange for their loyalty. She could present herself as a new hope for a more peaceful Westeros, which might attract these houses to her side.
Raoul could also be an ally. Despite his past with the Phantom, he might see the daughter as an innocent and want to help her. He could use his influence in society to shield her from the negative attention that might come her way once her identity is known.
His friends like Ron and Hermione would surely be his allies. They have always been by his side in the original stories, so it's likely they'll be there in the fanfiction too, helping Harry in his fight.
Hermione could be a strong ally. She's smart and could help Harry research more about battle magic. Ron too, with his loyalty and courage, would be by Harry's side.
Jiraiya could still play a role. Even if Naruto is raising himself, Jiraiya might cross paths with him and see his potential. He could offer some sporadic guidance without fully taking Naruto under his wing.
Percy Jackson himself could be an ally. Despite their differences, they both have a common goal of protecting the demigod world. His skills in combat and her intelligence would make them a great team.