We have moved a number of times since DD8 was born, and each time we let her take a little part of where we were leaving. For example, she has some sticks from her favorite tree at our last 2 houses, a paint stirrer with paint from her sister's bedroom (which she helped paint) at another house, some torn carpet from yet another place. Some rocks, whatever she really felt connected to.
We also let her go wild with her camera and got all of her pictures developed (yes, it is s film camera) before we left so that she could look at them on the trip to our new location.
We then have had to reexplain numerous times why we had to leave and why life at our new place will be just as good, if not better than what she had before.
We have found that it is actually easier to be the one leaving than the one staying behind when a friend moves. (Not that that is much of a comfort, but after a good friend of hers moved away even she realized that it was better to be the mover than the person staying behind.)
She also write letters to her friends from other places we've lived and we talk about them once in a while.
It can be tough, but it will all work out. (Lots of hugs and understanding empathy about being sad for moving away helps too - for both of you).
Good luck!
