My daughter was a LATE potty trainer. I thought that it would be so easy - as she made pee and poo on her potty chair when I first bought it and pulled it out of the box, back when she was under age 2 - but then not again for a long long time. She would scream, then finally, finally she started peeing on the potty, or a full sized toilet but she wouldn't poo. I was finally able to get her to poo on the
potty by bribing her! I had little treats, like refills for pez dispenser, colored pencil, etc. She wanted a Beta Fish in the worst way - we had babysat 2 for someone that I work with, and she really really wanted one of her own. I was so nervous that she wouldn't be potty trained for preschool (age 4) that I bribed her by saying if she went all week without pooing in her pants - that we could get the fish. She FINALLY told me that the reason she wouldn't go on the toilet was that she "was afraid of the plop". !!!!!! I simply put some toilet paper on the surface of the water and viola! Just like that she was able to go!!! :)
Good luck, I hope that these suggestions help! Keep me posted - I'm curious if the "plop" is what keeps other kids from using the potty for #2, or if my otherwise very bright girl is just weird! lol!