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.
Ruby might find an ally in a mysterious figure who has been waiting for someone like her to come back in time. This figure could have knowledge about the future and realizes that Ruby's actions in the past are crucial for the overall well - being of the world. There could also be a group of rebels in the past who are fighting against an unjust regime. Ruby, with her unique skills and knowledge from the future, could join forces with them. They would see her as an asset and she would have a group to support her in her time - traveling adventures.
One of her likely allies could be a time - keeper type of character. This character might exist outside of normal time and have the ability to guide Ruby through the past. Also, if there are any benevolent spirits or guardians in the past world she travels to, they could be her allies. They might be drawn to Ruby's good heart and her noble intentions of trying to fix or learn something important. Additionally, any younger versions of her family members could potentially become her allies if she reveals her true identity and purpose to them.