Hi, C.. Have you tried asking your daughter why she doesn't like to poop in the potty?
Is there a new baby in the house? If she sees that the baby gets to poop in the diapers, your 3.5 year old might have decided that she wants to get a little extra mothering by having you clean her up. Who gives her a bath? Maybe you could try giving her a little extra attention in the bath or playing with her more, and that will satisfy her need for extra attention.
Sometimes, very young children revert (go backward to baby behaviors) when something stressful happens to them. A new baby in the house, or a new house, period, or some other new and anxiety-producing change, can trigger that.
In the meantime, here's what I would do: stay calm, #1, and #2, make her help you clean up the poop! Calmly explain to her that the poop needs to be washed out of her clothes, and that the reason why we poop in the toilet is so that we don't have to touch the poop and wash it out of our panties, shorts, skirts, etc. CALMLY. Not as a punishment, but because she's a big girl now, and big girls can wash their own underwear. It may take a few times of having to do this, and she probably won't do it very well, but it's likely that after washing her own poop out of her own underwear a couple of times, she will want to put the poop where it belongs!
Again, don't punish her. Don't make a huge deal of it. Just very calmly get her little hands moving to do the job. She isn't going to like the smell, the feel, etc. And if you keep reminding her of where the poop is supposed to go, and that it goes in the potty so that no one has to wash it out of the underwear, she will get the message. At the same time, keep giving her good attention for other things that aren't related to poop at all.
Another thing that can be very effective is for her to see you going to the bathroom. Let her know how good it feels to make poop in the toilet, how proud you are of yourself every time you make it to the toilet, and so forth. And when she starts to do it right again, yes, give her all kinds of hugs, rewards, praises, joyfulness, and tell her what a wonderful girl she is.
I certainly hope this is helpful to you. I'm not a big fan of poop myself.
Peace,
Syl