Don't know if they'll expand on this later, but poor Aira chan really was innocent.
As a teenager, she was used to listening to her parents, when dragged into an unknown world and told she's to fight for them, she was scared. The prince seemed like he was looking out for her so she kind of imprinted on him, and relied on him. But as much as he protected her, he also isolated her.
Luckily the other adult is the saintess so now shes free to be a teenager again