What? No. She's still very much alive. If you had asked if it was his aunt's ashes, it would've been more believable and understandable. Check exactly four posts above yours.
No it has to do with a running tin foil hat theory that the stuff about the aunt is a lie. It is based on the parents evasiveness about the documents and the whole thing around it. Some say that it is the mother that is dying, others say it is a contract the parents have with John (you know that he has being buffing MC's mom).
Besides I think Abby already has her sister's ashes.