i am sure you don't want to hear it - but i think that she is too young to potty train...i think that you need to deal with the problem of her not enjoying a poopie diaper by changing her more quickly...but 20 months is pretty young to potty train. I will share with you what we did with our son - who is now 33 months old...
One year ago, just before he turned 2, we got a potty seat. He played with it, pretended to use it, occasionally did use it. Nearly 6 months later, just after he turned 2, he showed signs of being ready to make the move. We bought him underwear. Initially, he wore the underwear over a diaper and we took him to the bathroom nearly every hour. After a few days, he started resisting and saying he didn't have to go. We trusted his judgement, but would try again the next hour...After a week or so, we dropped the diaper (he had not had an accident in the diaper during the daytime in the first week). But, we still put a diaper on if we were leaving the house...some might call it a false sense of security, I called it avoiding a mess and embarrassing my son. It worked, and he had the control to tell us when he needed to go. Since January, we have had ONE accident - at home, that was partially my fault because I was doing something and couldn't stop immediately. He is not trained at night - which is fine with me, because in my opinion, sleep is more important!