My 17 year old sister stole my mom's car. Why didn't the cops charge her with car theft?

My 17 year old sister has been in trouble off and on for the last 2 years. Including two cases of ault. My sister decided she and her so-called friend wanted to run away. So while my mom was sleeping she went into her pocketbook and stole her car keys. They took my mom's car and she let the friend drive. The police stopped them for some reason and it was found out. The cops didn't charge my sister, but the friend(19) will be charged with theft. WTF! Why is my sister getting off scott free? She stole my mom's car and the police let her go like it was nothing. She said she is bored, thats why she took the car. Can you believe it? My sister even trashed my mother's house last year and the cops did nothing then. All because she is a juvenile. If she is adult enough to do adult crime, then she should do the time. My sister also has a substance abuse problem, which has lead to her baby being in Foster Care. My sister is on probation, but the judge doesn't do a damn thing and keeps giving her chance after chance. He says he can't make her go to Rehab. All he does is keep sending her back in for new court dates and nothing has changed. My sister needs to be punished and learned a lesson, but yet everyone is patting her on the head. Cops, lawyers, judges are no help. My mom is doing the best she can, but there is no father in the house. He is a crackhead himself and can't even hold a job because of his criminal record. I feel bad for my mom and it makes me angry how selfish my sister is.My sister will be 18 soon, then maybe she will be treated like a adult. Why do juveniles offenders get away without any punishment? If it was me, I would have been charged.