I'm not much help either I'm sure, but with Em we just let her go when SHE wanted to.... the sitting her on the potty frequently just caused us more arguements, so we let her do it on her own... sure there were a few mishaps but not many and we were far happier
Georgie pretty much did it herself (well for days at home - still haven't braved going out yet!), so she was totally different again!