S.M.
Hi, K.. Well, it's very fashionable among young people - even kids your daughter's age - to act this way. Chances are that there is a popular little girl, or a pod of popular little girls, who are acting this way toward the teacher and toward every other adult in the school.
Talk to the teacher, and let him/her know that your daughter has begun acting this way. He or she needs to #1 stop accepting this behavior from the kids in the classroom, because it's affecting the way all the kids deal with adults, and they're taking this attitude home with them.
You're going to need to be patient with your daughter. Keep disciplining her because if you accept this attitude at age 7, it's going to get horrendous pretty quickly as she gets older. I think you also have to try to figure out why she might feel this way toward you -- why the suddent disrespect. It sounds like it may be a combination of peer pressure at school plus the move to FL. She may be disappointed in how things turned out, especially if she had to give up friends, possessions, a room of her own, etc.
She's old enough to talk things out somewhat, at least on her level. Try asking her how she has felt since the move. She may not be so good at expressing her feelings -- the nasty attitude may be her way of not confronting those feelings -- but you might get a chance to coax it out of her if you're patient. Keep letting her know that you love her but don't like or appreciate the attitude. Keep praising her for things she does right, keep giving her attention for things done well. Give her some small chores to do and praise her for doing them well. That can get her focused on positive attention instead of the negative attention that she's seeking.
Also remember that girls are going through puberty younger and younger these days. It's quite common for a child to start menstruating at age 9; that means that the hormones are starting to kick in around 7 1/2 or 8 in order to get the body ready to menstruate at age 9!!! So she may be unlucky enough to have hormonal changes of this nature already, which only adds to the attitude problem.
I hope that you can restore the peace and loving atmosphere to your family very soon.
Peace,
Syl