tomorrow...

Tomorrow my boyfriend is playing cricket (Australian sport if you don't know) and I'm going to pick him up after work at 4:30 and he finishes at 6:30. This girl id going who is dating his mate but she is a flirt and she kissed him when we were dating. I hate her and I'm ashamed to say she was once a good friend of mine. Do I ignore her completely tomorrow? If she talks to me do I acknowledge her or just act like she's not there. If she talk to him what do I do? Do I be mature about it and ignore it (he hates her guts) or do I say something to her? Please help asap