Help! My 19 year old step-daughter is........?

...driving me and my wife crazy! She seems to thrive on drama and stand up for all that is wrong. After recently movong back in with her 8 year old sister, her mom and myself, she has been partying with neighbors in the apartment across the street. These people are supplying her with beer and pot. These people are also neglecting their 7 year old special needs son and 11 year old daughter. My step-daughter has made statements that she was going to contact DCYF and turn these people in for their actions. She had given us information about these neighbors neglecting the children by spending more money on pot and beer than for food, Easter gifts and doing laundry. Last nite my wife decided to call DCYF since they (the neighbors)had beat the 7 year old for taking his sisters snack. The police came and half-heartedly looked into the allegations and walked away. My step-daughter denied her statements about these people and stayed at their apartment because "she had no where else to go".