Aleu (Patreon)

While the rest of her siblings aspire to be like their father "The Famous Balto", she feels like she's caught in her father's shadow. She aspires to be nothing like him and wanting to be great in her own way. (Which is technically what the movie does, but does not do a good job at writing that.)

When she's younger she doesn't want to be a wolf and rejects that part of her, angry and bitter at things beyond her control. But when she gets older, she realizes that she's more at home in the wild.

But even being around humans had its perks. That part of her life actually made her more compassionate to other animals. Animals like the fox and the wolverine would normally be against accepting help from a wolf, let alone helping one. Since she showed them unconditional kindness, animals were more willing to help. 

Before she knew it, she was traveling farther away from home, coming across a pack of wolves. She sort of becomes a leader on her own among non-wolf animals, so this is new and exciting to her. And since she's the opposite of Niju, in becoming more adept to new ways of doing things and new ideas as opposed to keeping things the way they are, she gains popularity and rank within the pack, that she slowly transitions to living with.

Nava eventually trusts his pack to her, because his only other option was to entrust them to Niju, who would surely lead them to their deaths.

Aleu becomes leader and makes the difficult choice to leave her family behind to take care of the pack and cross the sea with them.