We know it wasn`t her Mom if this is true. She isn`t in Thailand,
Not really. We don't know that the person who is being arrested is the one who "did it"; could be an accomplice of some sort. The mother could still be either the killer or an accomplice, or even if neither, may have known all along who the killer was and for some reason didn't want to reveal it (she might have left a tell-all letter in a safe deposit box to be opened after she died, which would explain the timing).
Nope. She's not even on this Earth :( My curiosity is now peaked. Her parents always struck me a little weird. Feel sorry for her mom though.