what does "girls have their moods"mean?
“You could. Or Max, the currently time-outed Sellie and I could come up Friday evening, have a weekend at the beach and I can play with them.”
“Even better. But there’ll be no strawberries if they cause this reaction.”
“Usually she loves them, but girls do have their moods. I’ve got to go unshackle her, get us out of here. Send me what you can, and I’ll take a look.”
“Thanks. And . . . good luck.”

Question

what does "girls have their moods"mean?
“You could. Or Max, the currently time-outed Sellie and I could come up Friday evening, have a weekend at the beach and I can play with them.” 
“Even better. But there’ll be no strawberries if they cause this reaction.” 
“Usually she loves them, but girls do have their moods. I’ve got to go unshackle her, get us out of here. Send me what you can, and I’ll take a look.” 
“Thanks. And . . . good luck.”

Answer

Girls (and boys) have their moods. On one day, they might not feel like eating strawberries, because they are not in a 'strawberry mood' or 'in the mood for strawberries.' On another day, such as at the play date, the girl (or also a boy) might feel like and actually eat strawberries instead of rebelling and throwing them. So, a 'mood' in this context is a "A temporary state of mind or feeling" (Oxford Dictionary).

See also the Oxford Advanced Learners Dictionary: http://www.oxforddictionaries.com/us/definition/learner/mood