Well, a plot could revolve around Thor's internal struggle with her new identity. She could be in denial at first, trying to find ways to change back. But as time goes on, she starts to embrace it. Along the way, she meets a group of female warriors who teach her about the power and beauty of femininity in a warrior context. This helps her to fully accept her new form and use it to her advantage, whether it's in battle or in diplomatic situations within Asgard.
One plot idea could be that Thor, as a girl, has to navigate the male - dominated Asgardian society in a new way. She might face different expectations and challenges, like having to prove herself in combat even more so because of her new form. Another could be that Thor's relationships change. For example, his friends might be a bit confused at first but then learn to accept and support this new version of him. And perhaps she discovers new powers or a different connection to magic that was hidden before.