R.B.
I agree about her age, getting involved and staying busy, playing with what is familiar, talking on the telephone to who she misses, and allowing her time and space to miss what she has lost. Here is another thought: she may be allergic to something in the new house. Possibly the carpeting, new paint smells, or the pet cat the previous owners had, the new brand of bread you are buying because you can't find the same brand that you used to buy, or maybe the tree that is outside the window of her new room... she may be having an emotional reaction to a physical stimulus. Just another area to explore as you are Detective Mom trying to solve yet another kid mystery.
Good Luck!