It definitely sounds like Anevka may have killed her mother. Whether she also killed Tarvek's mother *could* be up for question: if they are far enough apart in age, it's possible that they are half-sibs. We don't know if Aaronev was married 2x or only once.

Other outre speculations: did "Mummy" try to make Anevka feel guilty about killing "Mummy", or about [possibly] killing Tarvek? Or did "Mummy" try to make someone else feel guilty about killing her?

I'd go with the simple answer, Anevka killed her mom, but with the idea that it could be more complicated.