Poop Issues

I suggest GrammaRocks' link as well. It's sound advice, and respectful of the child while putting her in charge of the decision.

I also had good results with my grandson, who had had a few painful poops due to constipation, to do role-playing with his stuffed toys and action figures. They each lined up before a small white bowl, complaining of needing to poop in turn, and were encouraged by me and my grandson to go ahead and try, promising they'd feel better once they did. So they each took turns, with much trepidation, grunted and strained, and "produced" a small pellet of clay. Then we would congratulate them, and the next toy would take his turn. This seemed to give my grandson, who was often sitting on the toilet during these games, the courage to take his turn as well.

My daughters both went through this stage, where they would poop in the diaper and pee in the potty. We made a chart and added a sticker for every (even attempted) poop in the potty, and after 10 stickers they could get something (I forget what, they are 11 and 14 now!). Rest assured, this is a phase, and she will eventually poop in the potty. Try a ring on the toilet perhaps if you are using a little potty to seem more "grown up", I recall my kids using that ring and a step stool and a comic book, it was better than sitting so low on a small potty stool. They have no lasting bathroom or emotional issues from pooping in diapers or the occasional outburst from their frustrated mom.

My guy (now a month past 2.5) was holding it as well. I followed the advice on this site:
http://www.rogerknapp.com/medical/pottytrainingrefusals.htm

and within two days he was telling me when he needed to use the potty to poop! The "power incentive" and how you use it (YOU own it, not your daughter, she earns the privilege of using it 30-60 minutes) was the key for us : ) I think your daughter is a good candidate for this approach.

We would let my little one blow bubbles in the house while on the potty trying to poop.

Just an idea maybe if you catch her before she starts to hold it, you might have better luck. Not sure if i'm explaining that right. but if you know she will poop at 2 pm than at 1:45 you put her on the potty. It's tricky since you said she usually poops at night. maybe try prune juice and see if that changes the rhythm of when she had to poop, so you can anticipate the awake poops better.

final thought, ride it out, sooner or later she will pass through this stage and be on to the next.

First off all kids go through this stage.

That being said, when she walks around holding her bum and saying that her belly hurts, we'd walk our kids into the bathroom and sit there with them reading books, playing eye spy, etc until they go. Even if that means 30 minutes.

Alot of kids don't like to poop on the big potty. we'd always have them sit on the little training potty then dump.

I do think that its a bit confusing to allow her choose a diaper to poop in then the potty.

It sounds like she's going down the right path, just keep encouraging her.
Sometimes the whole poop thing takes awhile to figure out.
Since she seems to like to go at night, I've read that a warm bath usually encourages the bowels to move. Maybe popping her in the tub just before bedtime and letting her know if she needs to poop you are going to put her on the toilet to do it will help her absorb that plan in her head.

Check out my most recent question. It is basically identical! I've gotten some great advice, so check it out! Let me know if you get any helpful hints :-)