M.H.
WOW, sounds like you have a ton going on(your bio). I'm not sure if I have the best advice...only what I would do.
I think her going through a grieving process is fine and probably healthy. Just keep reassuring her and maybe let her call her friend on the phone so she can reassure her she's not far away. Maybe even drive by and show her their new house because to your daughter they could be living half way around the world.
In the end she will be fine and learned a good'ol life lesson!
Good Luck!
M.