As absolutely wonderful as that would be, she couldn't. Or wouldn't, rather. Harry still needed her, and in a way she still needed him. He would survive the Triwizard Tournament if she had to burn the whole bloody maze to the ground. She had no illusions that his trials would end there, because obviously they wouldn't, but she would drag him through each one of them until he died a peaceful death in his sleep after a few centuries. He needed her.