If you are certain that you are moving then there isn't any real reason to wait. What for? She isn't going to be happy no matter when you go. So unless you are reconsidering the move entirely, then don't wait for her to "adjust".. unless by that you mean a few weeks or perhaps the end of this school year.
It is probably unfortunate that you didn't make this decision sooner, because 6th grade is typically the first year of Middle School and lots of kids are thrown together into new schools where they may or may not have their previous friends in their classes. It might have been a slightly easier adjustment for her to have started 6th with an entirely new bunch of kids in VA when EVERYONE was "new" at the same time.
But, since that wasn't the case, then putting it off further (until 8th grade? 9th grade?)... just doesn't make any sense to me.
If you are sure you ARE moving, then the question seems to me, whether or not to move NOW (as in in 2 weeks) or at the end of the school year. In which case there are 2 ways to look at it:
a) Your daughter could start "fresh" at a new school in August.
b) Your daughter could meet some kids (and spend some of her summer months getting to know a few of them) NOW, so that she knows some kids going into 7th grade in August.
Your daughter will likely want to put it off as long as is possible... b/c she will be hoping that the inevitable won't happen at all. Burying her head in the sand so to speak. Take your daughter's personality into consideration, and think about the real potential for her to meet new friends between now and May, and actually spend time getting to know them during the summer, and the possibility that she may not meet that many new kids and spend her summer alone. I'm thinking that she will meet at least ONE girl that she could be friendly with and hang with over the summer...
Good luck with your decision and helping your daughter adjust. My parents moved me in February of my 10th grade year. It was awful. But I survived.
:) I met a girl like me who had recently been transplanted and only knew a few other kids. We spend a lot of time together that summer. :)