Well Donna ~ I don't know for sure (and I don't have a crystal ball) but here's my take. This has nothing to do with your performance. She had someone else in mind for the position before you got there. They weren't available or her choice was vetoed. Now that person is available (or she twisted some arms) so they are in.

I would call her supervisor and request an exit interview. Tell them how much you enjoyed it and would like their feedback. A few months from now, your phone will ring. The person or persons they have put in that job will not have worked out because of this lady's "twisted" attitude. They will remember how professional you were call you up.

Even if they don't grant you an exit interview. Follow up with a letter to that lady's boss and thank them for the opportunity. Say, that you enjoyed working for them and are disappointed that you weren't the right fit.

Then go on with your life. Be positive. Who knows what the next exciting opportunity will be?