It was always possible that she was the one who couldn't be trusted. Perhaps she was blocking memories intentionally to protect herself from remembering all of the wretched acts she'd committed in the past. Uncovering her blocked and forgotten memory of the day she murdered Andromeda Tonks opened up the very real possibility that maybe she was the one to blame. She used to drink her potions like they were water. Not anything at all like the strawberry flavored ones that Antonin made her drink to calm her down when she was overwrought and confused, the ones she preferred were much more like Muggle heroin or possibly methamphetamines. She really didn't know much about the differences in the illegal Muggle drugs. Rabastan once forced a Muggle drug dealer to give them his product, but she couldn't really remember much of that time. It was all one drug-induced blur.