You don’t tell you daughter’s age
Most toddlers withhold stool because they have had a painful experience with passing stool. Children often respond and learn to relax when they receive reassurance and positive reinforcement. Also, take steps to keep stool soft, so the child can easily have a bowel movement when the urge develops.
It’s important the refrain from any negative reinforcement, comments and pressure.
Don’t overdo praise either as this can give a lot of pressure to perform
Avoid dangling legs; help them to feel secure sitting on the toilet.
The best position to poo is with the knees higher than the bottom
A child that is afraid to poo may develop constipation by holding the poo in at time; make sure you child drinks enough and has plenty of fiber in her diet.
Another reason why your daughter keeps pooping in her undies may be that she emotionally or physically isn’t quite ready yet

She will grow out of it

No real advice sorry as I am currently in the same boat with my three year old son. My neighbour said next time he poops his pants to hose him down and it won’t happen again although I’m not quite comfortable with this haha I have said to him today next time he poops his pants I will have to take a toy away as he needs to learn. Hopefully this works as nothing else seems to

With no age specified, it makes it difficult to give good advice.

You don’t mention an age. Most kids get the gist of wees on tge loo before poos. It must be the extra time on the loo that puts them off. Give her time she’ll get there

i agree may have to have a star chart or some incentive.

How old is your daughter? Some just take extra time. Charts and treats work for some kids but not all of them. I’m sure she will get there soon although I know the frustration of cleaning poo is enough motivation to try anything that might work.