Had you said "Daddy's girl" about Harper, would that mean anything? Or even Mummy's girl?
Mummy's boy (daddy's girl less so) can be used in a slightly less than positive manner to describe a young man, it would be a little disingenuous of you to suggest otherwise. This is why I ask the FM for a clarification on the point. They were polite enough to respond and clear this up. Sorted.