Hermione never told shown her letters to and from Krum to anyone.
Firstly, because it was none of their business.
Secondly, because no-one had asked politely. Oh, Ron had eyed one when she was writing in the common room, but she'd brushed him off.
Thirdly, because she had decided to learn Bulgarian, and she doubted whether there was anyone in the castle capable of deciphering her clumsy attempts at practising the language.
And fourthly, because if anyone had had a legitimate claim to read it, and asked to do so, and could read Bulgarian, they would be very curious as to why parts of the letters consisted of purple prose and dirty talk.
A girl had to keep busy somehow.
Fin