She needs to retain a local attorney as soon as possible. An attorney can evaluate the case and determine what is the. Ext best course of action. I tell everyone the sooner the better.
Please remember that this response was made generally to a general question posted on a web site. The advice was provided free of charge and is intended to provide guidance and encouragement for you to seek a practitioner in your local area. If you needed this assistance, that should show that the area of law you are researching is deep subject and open to possible multiple interpretations. Please go talk to a local attorney.
Your friend needs an attorney. Typically in Tarrant County, the DA is reasonably willing to listen to a fact scenario like you're describing, particularly if the driver of the car is truly willing to admit the contraband belonged to her. But your friend needs someone to go speak with the prosecutors on her behalf. At the end of the day, the State has to prove, beyond a reasonable doubt, that your friend possessed the substance. My job as an attorney is to do everything legally possible to keep the State from doing that.