Thank you for sharing your work. I thought this was interesting piece. Certainly, you did a good job meeting the challenge of the prompt. I think my problem with the story is that it could have used some more development. Your word count was 844; I think you could have made good work of the outstanding 156 words to smooth some transitions, and perhaps better build and express her incredulity. I know the word count is tight at 1K, but I just felt that Susan's reactions were a little abrupt. But that's just me.
One other thing: visually, your story could use some formatting. There is no spacing or indentation, and it makes it a bit difficult to read. I did not, however, see any errors in spelling, grammar, or punctuation, so that's a plus.
That said, please feel free to use or discard these suggestions as you see fit. You know what is best for your story.
Keep up the good work and write on!