I don't have any kids, but my OBGYN friend has 3 daughters under 5. she told me that she uses medical info to talk to her oldest about reproductive stuff. Shes already explained to her what sex is, how babies come about, and whenever she has new questions she already knows what ovaries and a vagina is. she also uses medical diagrams to tell them where privacy areas are and where no one should touch you, etc. Maybe using the same kind of language and pictures would be helpful in explaining pcos to your daughter?