What to do when your child lies?

My teenage daughter got in a lot of trouble recently for stealing an ipod at school. It was a big shock to me because I never imagined she would do something like that. We have tried to instill good values and morals in all our children. The sad part is I found out she lies about a lot of things. Now, I can't trust her. When we searched her room we found stuff she had stolen from us. Anyway, the ipod was recovered but the accessories were not. She says she didn't have them, but she also said she didn't have the ipod. She was suspended from school for a week and her grades will suffer. We have grounded her for the remainder of the school year, taken her cell phone, canceled her facebook, etc. But she has been lying to us again. What can we do? When I asked why she stole it (she had an ipod), she simply said she didn't think she would get caught. I asked why she stole the other stuff and she said the same thing. I don't know what to do. These are big lies and if she had been an adult, she could have been charged with grand larceny. Any advice is appreciated.