The princess used to hear flora sing at parties, so she starts singing the same song about a girl going every night to the stables, the implication being that she goes there to have sex every night (or is possibly taken there unwillingly since it starts with "the poor thing"). The princess asks her why the girl in the song goes to the stables every night but she's embarrassed to say it. The princess then asks innocently if it's to sleep with the horses so flora says yeah sure that's it. Then she asks why the girl gets stretched, meaning the next part of the song says that, which again implies that she's getting fucked. Flora's even more embarrassed as she doesn't know what to make up so she doesn't have to tell her the truth of the song.