Police say Rivera guided the girl, advising her on whether the knife she had was enough to do the job.
A judge has ordered a 15-year-old girl and her 23-year-old boyfriend to stand trial on accusations they plotted to kill her family.
The woman is accused of killing her husband, shooting her daughter and pointing a gun at her son during an argument.
Prosecutors say the plan was to kill the girl’s brother, sister and parents so she could run away with her much-older boyfriend.
Police say Sikorski and her boyfriend, 23-year-old Michael Rivera of Detroit, conspired to kill her family members and run away together.
The man allegedly formed the plan with his younger girlfriend to “get rid” of her parents, who were reportedly trying to keep the couple apart.
A 46-year-old man will likely spend the rest of his life behind bars, convicted in the attempted murder of his mother last August.
“He said … ‘Mother I’m going to kill you. You’re going to die. You have eight minutes.'”
The 30-year-old victim called police Friday, accusing Charles Anderson of strangling her until she was unconscious.
Three men and one woman are facing several charges, including attempted murder and home invasion, in what police are calling the botched robbery of a Bloomfield Hills attorney.