I bought theatre tickets for a group of friends. Everyone has paid me back apart from one person. I have messaged her twice with bank details and reminded her when we met up for the show. I'm fairly certain she doesn't have any money problems and she is generally on the ball, efficient and trustworthy. I don't know how to approach this. Can anyone think of an assertive but friendly way to word a request to pay up? It's quite a lot of money for me?