Not to be a smartass, but once she mentioned that she burned/disposed her mom's stuff in the mountains near her grandparents' house, I made a mental note that the MC should have realized that she just revealed a prime location to investigate.
Her line "They didn't have anything to do with me" was the only conflicting addition that made me think twice. Does she view the remaining body parts in the same twisted way she views her mother's existence? Or maybe what's hidden there is proof of her innocence that could only be perceived positively if discovered by a third party. That would make the line make more sense.