[aisle] Need Help With Title

[Crystal Roel]

Hello group,
I have a 5th grade student trying to identify a book they wanted to go back to. Here are the descriptors that she thinks she remembers:

- Trilogy
- A boy and a girl, one is supposed to be a knight and one a wizard and they want to swap roles
- 1st book cover has a white horse (no human characters)
- 2nd book cover might have an owl on it

Anyone know what book this is?

Crystal