How do you deal with a child who, despite being reassured that she's doing well, gets frightened and tries to climb off the potty in the middle of a bowel movement?
Firstly, come what may, try and gently hold her on the potty until she is finished with the bowel movement. If she will let you do this without becoming overwhelmingly upset, then her rush to get off the potty is probably just more the shock of the new experience and not an extreme fear. Help her to sit a few times and she'll probably be fine. You can say, "I know it's a little hard for you, but you are doing a great job and I'm going to help you sit until you are finished." Of course if she does so she deserves quite a significant reward.
If she does become very upset, then she may not be ready for this step. If she is under age three and has not yet established regular ability to urinate in the potty, then hold her in place until you clean her up (if she is making a mess by getting up in the middle) and then you can have her continue the bowel movement into a diaper. Tell her that you are proud of her for "starting" to have a bowel movement in the potty and that you are sure soon she'll be ready to finish. Drop the issue until she is totally trained for urine.
If she is three years old and is totally toilet trained for urine, try to set up with her a separate program for bowel movement training. Make a chart with her (as I described in the Time Out article) and discuss what she wants as a reward once she makes a whole bowel movement on the potty. Let her know that getting up in the middle can make a mess and that you cannot allow her to do that.
Feel free to physically help her to stay on the potty. As soon as you see she is starting a bowel movement, put your hands on her (being as gentle as possible) to try and prevent any initial bolting. Tell her "You are doing a great job, just sit for a little bit more." I do not suggest, however, physically forcing her to sit if she is very actively opposing you.
Try this method for a while and see if there is improvement. My gut feeling from your letter is that your daughter may have been scared off by a new experience. Let her adjust to the new experience gradually and without pressure. If, after several weeks, this method is not working for you, please let me know how things stand and I'll be happy to give you further suggestions.
Esther Boylan Wolfson, MA