As long as you are sure you have to move I say move now! As she is in school longer she builds friendships that will be hard to break and it may be harder for her to make friends in her new location because established groups and friendships have formed.
You are in a good position to move now. In first grade, you are still in a position to help her make friends - it's still appropriate for you to call other moms and set up play dates for kids she is interested in know better. You will be in a much better position to HELP her make new friends in 1st grade. Once she is in 3rd or 4th grade, it's no longer appropriate for you to call other moms and set up play time. They need to do it on their own.
Here is what I would do. Move this summer. As soon as school starts, get the student directory with all the names/addresses/phone numbers of the kids in the school (even if they haven't published a new one get it for the previous year). A while after school starts and she has started to get to know the kids better, start calling for play dates. This is how you can help her adjust to her new school. For her current friends, offer to be pen pails if you are moving too far away, or make an effort to drive to them a few times to help her adjust.
Good luck!