Your daughter is still well within the "normal" age range for potty training. It's great that she is doing so well with the "pee" component. Plenty of kids have a harder time with pooping in the toilet, and it's helpful to treat it as an entirely different stage of training. I know a few young families whose kids continued to ask for a diaper for pooping for several months after pee training was successful. It did not appear to confuse the children, who can be pretty sensible about what will work for them.
The urges and sensations for pooping are different, and can be complicated by strain or pain, diarrhea or constipation, or swing from one to the other. It usually takes a lot longer to poop than to pee – my grandson gets pins and needles in his legs by the time he's done. Some kids are very regular, some never know what to expect. So it's often much harder to figure out the pooping, and this isn't your daughter's fault.
It's not unusual to develop fear of the potty, or the sensations, or feel scared when they see a "part of themselves" in the potty and see it flushed away. This fear is hard to reason away in a young child, but usually they outgrow it when their cognitive functions are better developed. Parents can sometimes help this by realizing that the fear is real, and perhaps cheerfully encouraging the child to flush when the parent has a bowel movement. And explanation of "when food goes in, poop must come out" can be useful.
Most developmental specialists suggest that children be allowed to approach this challenge at their own speed, with parents acting as coaches, personal assistants, and cheerleaders. If the whole activity has not deteriorated into a power struggle, kids do use the potty willingly when they are matured enough physically and emotionally. Then children are as proud as they are with any other new skill. Many parents report that any stage of training can take from one day to a couple of weeks when the child is confident he can do it.
You might try introducing a new support activity or game. If your daughter tends to poop at a regular time or you can tell by her body language that a bm is on the way, you might ask her to sit for a while and read to her, or line up a few of her toys to role-play successful pooping (my grandson still loves this if he's having an uncomfortable poop.) We actually started with the puppet games before he ever tried to poop on the toilet, so he was already connected with that. I also used to dramatically "clear all the dinosaurs out" so there would be room on the toilet seat for him, and he loved the imaginary competition, requiring me to keep the critters away until he was done.
If you do get your daughter to sit and try, don't expect immediate results. There's still a huge emotional component along with the physical sensations, and anxious or angry children are known to withhold poop, often not even intentionally. They are just too tense to poop. So, if she's successful, be pleased but not overexcited for her, and don't assume it is necessarily anything more than a happy accident yet. After a few repeats, she'll probably start to get the "sequence of events" figured out.
If she's not successful, just cheerfully appreciate her trying, and express your calm confidence that she'll be able to do this pretty soon. She will. It just takes some kids more time, and the more pressure she feels to succeed, the less likely she is to get in touch with her actual bodily sensations. I've also personally been reluctant to use rewards for a natural function, but some parents find they help, perhaps more so in the case of emotional resistance.
A couple of moms I've known used diaper liners in the underpants, and found they reduced the cleanup tremendously.
Please be as patient as you are able with your daughter. She's not going to train any faster if you seem tense, angry or disappointed in her.
