Your interviewer isn't asking this question because she wants to know about that time in college that you had a paper due but your cat got a stomach virus and your car broke down. What she's really asking is "Tell me a time that you succeeded under pressure". You'll want to answer it without framing it as a "woe is me" story. For instance:

"In my last position, we were working on a very strict budget and close deadline. Because we were skilled communicators, everyone was able to pull together and exceed client expectations when the presentation was rescheduled to a week ahead of time."