Sounds like a positive outing to me. It's sad that people behave differently when they think a police officer is present. We're all tasked with the job of maintaining our communities, not just the boys in blue.
Also, just to be really pedantically annoying, you probably prevented a battery from occurring. It sounds like she probably assaulted the guy when she spat at him. You can assault with somebody with words alone, they just have to feel threatened (I believe).