We had this problem with our Daughter too (pees in toliet but poops in her diaper)...She started training herself at 18 month and then just stoped!! We got her going again at about 3 1/2 years and we tried everything!! We KNEW she could do it, it was just a matter of her wanting to. We took toys away, bought "potty prizes" for when she did go poop in the potty, offered stickers, had charts, the whole 9 freakin yards!! lol But it took my Husbands mom to offer her a sleep over when ever she wants as long as she can go potty in the toilet, no diapers allowed, that she finally started to become totally potty trained. 2 weeks and she was done, no accidents or anything!
Maybe you could offer her something she REALLY wants and tell her that "only BIG girls can have those" like a sleep over, that new toy or going to a movie at the theater.
Good Luck!!