Hearing Tracey deny it, Heidi didn't know what to believe now. IF Ginny was right, it wouldn't be a stretch for Tracey to be lying now, but if she wasn't then everything was a big mistake or someone else was lying.
As Tracey told of her alibi, Heidi rubbed her temples. She might have to ask Megan. Maybe even Snape.
"I don't know what to believe, Tracey." Heidi whispered softly. "Either you're lying or Katie or Ginny are." But why would Katie have lied to Ginny when she confronted her and said it had been Tracey in her bed if it wasn't? Heidi was so confused. She wanted to believe Tracey, but her trust in the girl was still shaky from the events at the party.