Of course her parents would be involved in a plot to nail someone that hurt their daughter, it goes on all the time.
Prime example: Laura Wallen's parents did it, publicly and on live television.
In their case a calculated decision was made by LE to do this press conference along with her parents who were in on it. They wanted to see what her boyfriend would say and how he would act. Her parents went above and beyond to get her boyfriend Taylor. The mother even held his hand and her father was patting him. ALL STAGED. Her body was located a short time later and he was arrested.
You can watch it here and listen to the report they will tell you it was staged. Does it matter if you plot against your child's killer, POI, to obtain info?
In these cases the rules are: there are no rules or social graces.
http://baltimore.cbslocal.com/2017/09/13/police-missing-pregnant-teacher-found-dead/