The story is simple - girls are trying to pair her friend Isabel with a handsome lord. Isabel is not so happy about that. But what does it mean "have cowslips between their ears"? Suppose, it is some kind of idiom. Does it have any synonyms?
“Your lord shan’t enjoy that.”
Isabel did not pretend to misunderstand. “He is not my lord.”
“Gwen and Lara would have it differently.”
Isabel’s brows snapped together. “Gwen and Lara have cowslips between their ears. I won’t be thrust at him, Jane. You might as well tell them as much.”
Sara MacLean "Ten ways to be adored when landing a lord"