Dumbledore could also be an ally in the background. He may not be directly involved in the day - to - day care of the dragons, but he could provide Hermione with the necessary permissions and protection. His vast knowledge of magic and his influence in the wizarding world could help Hermione avoid getting into too much trouble for her dragon - caring activities. Additionally, some of the older and more experienced wizards in the Care of Magical Creatures department at Hogwarts might offer their assistance, albeit secretly.
Neville could be an ally too. His skills in herbology could come in handy when it comes to finding the right plants to feed the dragons or to use for medicinal purposes. Also, Luna Lovegood might be involved. Her unique perspective and knowledge of strange magical creatures could give Hermione new ideas on how to care for the dragons. She might know of some obscure spells or methods that are beneficial.
Harry and Ron could be her main allies. They've always been by her side in the original story, so it's likely they'd support her new adventure as a dragon rider. They could help her keep her dragon - riding activities a secret from the teachers at Hogwarts.
Perhaps Hermione gets involved in a dragon - breeding project gone wrong. She has to care for dragons that have some genetic mutations due to improper breeding. This could lead to her researching ancient dragon - care spells and potions. Or, she could be in a situation where she has to teach dragons how to fend for themselves in a changing magical environment, which would involve creating special training regimens.
Harry and Ron could be her obvious allies. They've been through so much together, and if Hermione has a reason to get revenge on the Order, they'd likely stand by her side. They trust her judgment and would be willing to help her out.
Dumbledore could also be an ally. He is very knowledgeable and might give Hermione some advice or information about the vanishing cabinet that she needs to successfully sabotage it. He might also provide some protection if there are any risks associated with her actions.
One possible reason could be a misunderstanding. Maybe her friends thought she was following but she got distracted by something, like a new spell she saw in an old book. So they unknowingly left her behind.
Another possibility is Harry Potter himself. This would be a very different take on their relationship. In some fanfiction, the strong bond between Hermione and Harry could be taken to a new level. Maybe in a situation where they are the last hope for the wizarding world, they conceive a child in secret to carry on some special magic or power that could save the wizarding community.
Sakura could be one of her main allies. Even in a samurai - themed story, Sakura's medical skills and combat abilities would be useful. She could support fem Naruto in battles and help heal any wounds.
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.
Definitely Naruto first. Then there's Tsunade. As the Hokage, she could be a powerful ally. She could provide resources and political support for the female Anbu commander. Rock Lee could be an ally too. His determination and physical strength could be helpful in combat. And Neji, before his death, could have been an ally. His skills with the Byakugan would have been useful for surveillance and combat support.
Her friends from her own time could potentially be her allies even when she goes back in time. For example, if she has a special bond with Weiss, Weiss might be able to sense Ruby's presence in the past in some way and offer help. Another possible ally could be a character from the past who she befriends, like an old wizard who recognizes Ruby's special powers and decides to help her on her mission.