So you just sacrifice "druggies" instead, their lives have no meaning, right?
Druggies have made their choices. They chose to do drugs. This one chose not only to use drugs, she chose to sell them to other druggies. She probably got herself into hock with dealer at some point and that is how she wound up dealing, but she still had choices. She could have left town without leaving a forwarding address. Instead, she then gets caught dealing.
The cops offered her a reasonable deal. In exchange for four years of her life that they owned at they point, they told her they wanted the asshole that was distributing the drugs. She could have done the four years. After she agreed, she should not have done anything at all that put her outside of their protection. She did. Again, she made a choice.
I've seen it more than once and my family is full of cops, and one or two druggies.
Granted they need to execute the person who made the choice to kill her as soon as legally possible.