When our son was 11 years old his very close friend of many years moved with his foreign parents permanently back to their home country. We, his parents, believe this event left a permanent mark on the way he engages with people. Although very few, if any, would discern it (but we feel we do) we think he is much more guarded and that he is protecting himself against the risk of feeling such a loss again - he is not as open or any longer as readily friendly as he was. His older brother would not have reacted the same way, we believe - it is a matter of what each person is like.
Make certain your daughter knows of the coming move, if she doesn't already. I suggest worrying too much about this will rub off on her and amplify any sadness in her mind, you should not brush it off either because that would be insensitive - keep a balance. If/when appropriate, point out that it is easy to keep in touch, as people do all over the world - compare with the way things were not long ago when people moved to the Americas, Australia, etc. and sometimes were never again able to see their next of kin (parents siblings) and communication was limited to a single handwritten letter every few months. Separation has been part of life since the dawn of time - but don't mention the comparison with death.