Why is it used "is" not "has"?
Native speaker’s answer
Rebecca
In this case, "is" is used to mean something similar to "exists." Thus, we can understand the speaker saying "inside every girl is a castle-storming ... adventure lover" to mean "inside every girl exists a castle storming ... adventure lover." The speaker means to say that this type of character is hidden inside every girl. "Has" would imply possession, which changes the nuance of the sentence. "Inside every man/woman" is actually a common expression used to express that there is a hidden character or desire inside everyone. Ex: Inside every woman is a girl who once dreamed of being a princess. Ex: Inside every man is a struggle between good and evil.