First, I'm sorry for your loss.

Is she going to the wake and/or funeral, right? She's going to figure out something when she sees the urn, so I would just tell her the truth. That there are 2 ways in which a body can be "buried" after death, either in a casket in the ground or the body can be turned into ashes. And that some people prefer being turned into ashes for lots of reasons, like wanting their ashes spread in places that they love, like at sea or on some tropical beach or into the wind or in this case, possibly up in Alaska.