When Turtle says her mom's head is in the clouds with Amelia Earhart, there's two things to understand. First, the phrase "head in the clouds" means that someone is not thinking clearly about a situation, not paying attention, or sort of daydreaming.
Next is knowing who Amelia Earhart is and why she's in the clouds. Amelia Earhart was a famous pilot in the 1930's. She set many many flying records for female pilots for distance and speed. During Turtle in Paradise, she would have been very famous.