That's pretty sad. I have a bunch of these kind of situations where I could have reacted a certain way - or at all - where as in reality I didn't. Tons of times where I think of a past conversation and wish I'd said something different - or at all.
These things happen, and the important thing to do is learn and be aware next time.
Also, in a way, the experience may have made her a little bit jaded/ closed off. Or, the situation could have had a positive effect on her life, like learning not to do something nice to expect nice stuff back in return. To be able to give a smile, a wave, and shine some light into a strangers day without expecting them to do the same.
Often times, things that seem negetive on the surface can actually be pretty positive in ways we'll never know.
It's funny how a snap moment can make one think so much about life and relationship. And I guess I'll never know what, if any impact this had on her, hope none negative.