H..
Trust is hard to talk about- you have to show her. My daughter was caught lying about brushing her teeth, so the next time I sent her to brush them, when she was done I asked, "Did you brush your teeth?" She said she did. I said, "I wish I could believe you but you lied last time and I don't want you to have rotten teeth, so go brush them again." Then I followed her to watch her do it. I'm pretty sure she had really brushed them already, so she had to brush them twice, which was inconvenient to her. So now she doesn't bother lying about teeth brushing because she knows the consequence isn't worth it if she gets caught. You have to think on your toes and have logical consequences for her lying that will be inconvenient for her. Good luck! I think it's soooo important for us to build a trusting relationship (both ways) with our tweens before we wake one morning and find they are suddenly teenagers!