As Ron led her down the tunnel from Moaning Myrtle’s bathroom she reached out for her bond with Severus, but she could not feel him.  He was blocking her.  She tried for Lucius but felt nothing.  Perhaps the wards around the castle were interfering, or perhaps they were all deliberately blocking her.  Then again, it could just as easily be Hogwarts itself, the castle was a vast source of ancient magic and had its own wards and protections.  She hoped they were alright.