Sydney has had some intestinal issues whether due to her not wanting to go or simply not being able to. One day, after having not gone for a 3 days, one of her teachers at school sat her down and explained the importance of pooping. Sydney immediately went over to the corner and pooped. It was at that point that we realized she was intentionally holding back. We think she's had a few legit bouts of not begin able to go and it hurting when she finally did go which led to not wanting to go at all. During some of the worst moments, she would cry and tell us to change her diaper (without having gone yet). There were also two cases where rock hard poo got stuck halfway out and we had to "help" her. Not fun.
Anyway, with that background in mind, the potty weekend in question was one following a multi-day poo drought. She cried. She begged us to change her diaper (which was clean). Eventually we put her on the potty and shortly there after a look of shock hit her face and a huge poo came out. Meghan and I praised her, got her cleaned up, and moved the evening forward with a bath. Sydney however was NOT happy. She was clearly upset and somewhat traumatized. We opted to stop talking about it all together because initially it was just making her more upset.
The following day we brought the topic up and Sydney was more receptive to the concept. Later that day, she even did it again. Meghan may be able to describe the facial expressions involved better than I can. After that Meghan went out and got her some pull ups, and we've been actively trying to potty train ever since.
It's worth noting that aside from a few dribbles of pee and the two poops mentioned above, Sydney has done a LOT of sitting on the potty but hasn't accomplished much. She typically wants to sit on it right after she pees and her diaper gets wet.