ASTRIA REGULUS BLACK found Ginny Weasley later that night, however, the younger girl appeared to have no recollection of the fight, no matter what Astria said. And when Astria continued to ask her questions, she learned Ginny hardly had any recollection of the week at all. She didn't remember yelling at Luna nor Neville, and she seemed to be completely oblivious to the fact she dragged Astrias unconscious body down a hallway and into the girl's lavatory.
What bothered Astria was Ginny didn't seem to mind this fact. In any normal instance where someone forgot everything for most of a week or anything they did, a person would be distraught. But the redhead didn't look like she cared, not even confused, nodding and humming along to whatever Astria said.
Astria decided it had something to do with that book, the same book she had seen with Ginny throughout the year, and the same book Harry Potter walked away with. And now Ginny had ridden herself of it, she still had bloodshot eyes and looked a ways from well, but she was far from acting the way she did before.
Neville had asked many questions when he arrived in Myrtle's bathroom and hauled her back to her dorm, much to his distaste because he wanted to take her to the medical wing, but Astria refused. Astria also didn't see the sense in lying to her friend at the time and explained what happened, leaving bits here and there out. The part where Ginny knocked her out with a powerful spell was left out, instead, Astria told him she had run into the bathroom after the girl and slipped, hitting her head. It was written all over Neville's face that he didn't believe her, but he didn't ask anything else after that.
However, now that Ginny didn't remember her actions, Astria had some real damage control to do, starting with Luna Lovegood. But the idea of lying to her friends again, and making some sort of excuse for Ginny up sounded wrong. And Astria found herself stuck.