D.G.
My daughter was the same way around 20 mnths sometimes she would go on the potty. Everytime I went to the bathroom I let her sit on her little potty (even if she had her diaper on) then everytime I changed a diaper we would go sit on the potty just to get the idea of what it was for. Then right after her 2nd birthday a friend told me how she trianed her kids and I tried. You do all the work at first but it really works. For the first couple days you bring them to the potty every 15 to 20 minutes then after a few days you bring them every 30 minutes, I skipped the every 45 minute step because after a week and a half my daughter started telling me she had to go potty.
I just started with my 2 year old son and he is getting the hang of going potty in the potty. I have him run around in shorts without a diaper and he has been going in to sit on the potty. He doesn't always go but he is getting the idea of it. When I had the diaper on him he would pee in the diaper then take it all off and go sit on the potty.