Outside North America, people relate to strangers in public. I prefer societies that do. Their social fabric is stronger. Had I been the OP, I would have heard the woman out once fully. I certainly would never tell a person that his problem doesn't interest me unless he were hassling me for money or represented a threat to my safety.
There are so many ways available to express empathy that take no time. Usually, people only need from you some signal - a physical gesture, a facial exp<b></b>ression, or a few words - some response to show that you recognize their predicament (or even just their presence in other situations). Anything that expresses a little warmth and understanding works. If the person still goes on after you've done that, i's fine to interrupt him squarely by saying that you must leave now, ask to finish your business with him, say goodbye with a smile and leave. Portenos do this. Here in France where we now live, the same level of care and sociability is also expected of every demographic and of every age from 7 to 90 in public whenever you happen to come into direct contact with anybody. They almost all do it. It's just normal good manners, very important and lets everyone know they belong to something larger than only themselves. Just as in BA, doing this here is grounded in the premise that nobody can be too busy as an individual to be gracious to any other if a society wants to remain one.