Does she have any reasons you know for being upset about something? I'm not saying that is any excuse for her behavior, but it might give you a place to start from.
I would sit down and talk to her very specifically about what you have noticed. Say something like, "Yesterday when Susie was here you told her she looked fat, etc. I am wondering why you would say something like that to your friend, when it so obviously hurt her feelings?"
If she somehow tries to justify her actions or behavior "Mom- I was just kidding, she knew that! " or "Everyone acts that way, we're just goofing around!" You need to make it clear that you don't care how OTHER people behave or what they say or do- you expect HER to behave a certain way.
Ask her how she would feel if her friends did these things to her? if she says they do, ask her if that makes them better friends? Good friends are GOOD to each other- they don't say mean things or kick each other ( that sounds more like something a toddler would do!!) even joking. Make it clear that if she keeps acting this way, she won't HAVE any friends after a while- they will not put up with this treatment from her!
Ask her what kind of friends she wants to have going into high school- girls who support her and love her for who she is and share interests with her? Or a bunch of slaves she can boss around and pick on? Warn her that 'mean girls' very seldom have a happy high school experience- or a happy life after that. Most teens don't want to be seen as the 'mean girl' - but they are good at explaining away their own bad behavior and need it pointed out to them sometimes.
As for lying to you and your husband- a few fibs here and there are bound to happen. But if she is consistently lying about things, you need to confront her. Ask why she felt she had to lie. Make up specific punishments for being caught in a lie- she does not get to watch her favorite tv show, no texting or phone privileges for 2 days, no sleepover or movie that weekend, etc. Make sure she knows VERY clearly that any time she tells a lie, she risks those specific punishments.
Tell her that you WANT to trust her. You understand she is getting older and wants more freedom, etc. but you can only help her IF she meets you halfway by being worthy of your trust and PROVING she is mature enough to enjoy more privileges. Tell her that being honest AND treating her friends well are ways that she can show maturity to you.
Do not be afraid to be THE MOM, here! At this age kids want more freedom- but they also want to test the rules and be reassured that mom and dad are still on top of the situation. Good luck- I think it will turn out ok, just don't be afraid to have a talk with her as often as possible and make it clear that her negative behavior will have negative consequences!
