Switching schools in the middle of the year can be a real shock, it's true. My parents moved a lot so I did it a few times, but later in life (6th grade, 10th grade). I think that's probably much worse. If you can avoid moving at that time, great, but if not, I'd say visit the school she would be going to before the move. I know you'd have to take some time off work, and she'd have to take time from school, but it might be worth it. Perhaps the principals/teachers on both sides could help you with ideas re. the transition.
Also, involve her in the move as much as you possibly can. Of course, she can't decide IF you're going to move, but giving her some say in parts of it will give her a feeling of control and will probably help a lot. My parents "sprang" a couple of the moves on us, which was also awful. You don't have to share the gory details of adult life, but kids aren't stupid and they need a framework to work with.
Good luck with your house hunting!