Pooping toddlers

So im due on december 6th. Hubby and i are trying to potty train our kids before our little girl gets here. Its been pretty successful with our 2 1/2 year old son. He both pees and poops on the potty. Our 3 year old daughter is a different story. She pees on the potty just fine. She will poop once in a blue moon on the potty. Any other time, she poops on herself, tells me afterward and smiles about it. We are so frustrated. We have tried snacks, showing her how to grunt to get it out(thats how we did with our son and he caught onto it pretty quick) Is anyone currently going through this with little girls? Or is mine just not catching on/doesnt care? My father in law thinks she will stop pooping on herself when she gets tired of it. But thats what im afraid of. We want to put her in school next august since she will be 4 in march but she is nowheres near ready if she cant poop on the potty like a big girl. Please no judging. Im just a frustrated momma here trying to get her to grow up a little