She was probably just very frustrated that you messed up her schedule/money for the day. You say you've seen her before, so chances are that she may have turned away someone new to see you because return clients are always more stable. Of course her reaction wasn't the best, as you get more flies with honey than vinegar. I would maybe give it a few days and see if she offers up a sincere apology.
Like a few others have said, the cops are everywhere. That's what they do. I see probably a cop every five or ten minutes these days, whether I am at home or up at the incall. They drive through all the apartment complexes at random, and park places and "watch" for no apparent reason. Well the reason is to deter crime, and see it works, worked on you!
If there is one cop or even a group of them at an apartment complex where you are going to meet a lady, I would say please contact her before you bolt. If they are not there for you or her why let it ruin y'all's day? Hopefully they are just there arresting drug dealers, thieves, or child molesters, something I actually DON'T mind paying my taxes for.
But when all is said and done, if you were spooked and feeling freaked out the session probably would've been bad anyway, so you were better off to leave. It is just unfortunate that both of you (you and the lady) had to suffer for nothing.
Hopefully this thread will help ease some of the freak-out factor and can keep this same scenario from happening as much!