How do I catch my friend in a lie?

Few weeks go I heard her and my other friend talk abt me i couldn’t quiet catch what she was talking abt but the moment I got in they got quiet and when I got back up they were giving each other signals Ik it a shit talk but something they wouldn’t say to my face I confronted her on text few days ago she said she doesn’t remember then texted me back and said that the other girl was complaining abt her friend w the same name as me who was gving her the cold shoulder and now she has to go on a bus which I literally heard few days ago on our last day of our final (so she used another story to cover up this) I think she lying but idk how to catch her