Police Pressing Young Woman To Do A Controlled Buy Under Sketchy Circumstances?

My girlfriend was pulled over with a friend who obviously was under investigation. She had a pipe on her at the time. In missouri it is only a misdemeanor paraphernalia ticket. Two officers waiting for all the other units to leave then threw her in their car and drove her to a parking lot where they proceeded to intimidate and scare her in an effort to get her to do a controlled buy of narcotics. They didn't tell her what charges were being leveled against her, didn't read her Miranda rights or tell her she was being detained or arrested. They also were talking about testing for a promotion with the department right in front of her. I'm thinking these are two questionable officers trying to ride the coat tails of a larger investigation to try and scare a woman into making a case for them. What is the legality of this situation I'm Missouri. I'm am in the process of getting her a criminal defense attorney. The officers said they will text her and she doesn't respond a few days after the text, "things won't be good". Any thoughts and advice is greatly appreciated. TYIA