You could start with the female OC being lost in the Digital World and having to find her way back home. But as she travels, she realizes that there are bigger problems in the Digital World that she can't just ignore. So, she teams up with the DigiDestined. Her unique skills, whether it's her ability to communicate with certain Digimon or her knowledge of some hidden Digital World lore, help the group in their adventures. As the story progresses, she grows not only in power but also in her understanding of the Digital World and her place in it.
A good plot could involve your female OC having a connection to an ancient Digimon prophecy. She discovers that she might be the key to fulfilling it, but she doesn't know how. Along the way, she forms strong friendships with the other DigiDestined. They all help each other out in battles and in solving the mysteries of the prophecy. You can also add some twists, like a false lead that makes her think she's on the wrong path for a while.
First, give your female OC a clear goal. For example, she might want to find a way to bring peace between two warring factions in the Digital World. Then, introduce obstacles that she has to overcome. Maybe she's not trusted by some of the DigiDestined at first because she's new. As she tries to achieve her goal, she could face challenges like powerful enemy Digimon or difficult terrains in the Digital World.