9 year old

I am so frustrated with Christy. Last night we put her to bed and then David and I ran an errand. We were gone for 15 minutes. So this morning when it's time to take Christy to school I check her pockets to make sure she isn't taking something to school that shouldn't go. Lo and behold what do I find in her pocket...... 2 of my rings. I guess last night while David and I were gone Christy went in our bathroom and dug thru my jewelry and took two of my rings. I asked her why and got the same response I get to every other question I ask "I don't know"!!!! I have had it. She is almost ten years old we should be able to trust her. Last time we were in St. George (not just last weekend the time before) Christy was over playing with Kayley. When we came home I was cleaning out her suitcase and found one of Kayley's toys, when asked why she took it Christy said " I don't know". It is so embarrassing for me. I am surprised that we are still allowed in any family members home. I am pretty sure at one point or another Christy has stolen from them all. And it's not like Christy doesn't have her own stuff. She is spoiled and always has been. She has more toys than room. She has art stuff flowing out her art drawer. She seems to have everything and she gets allowance too. I don't know how to help her to stop. We had her talk to the Bishop once, I guess it didn't help. Christy also has a big problem with lying. I am at the point where I don't believe any words that come out of her mouth. I just don't know what to do anymore. No punishment seems to have any effect on her either. I'm stuck. When I have the baby I am going to have less time with Christy. I know that I am not going to be able to watch over her every minute. I just don't know what to do anymore. Does anyone want a 9 year old?