We did the 20 minutes sit on toilet with our first son and, to be honest, it became a management problem since we were forcing him to do it on our terms rather than on his own. We did not use any diapers (or barely any) and stressed him to use the toilet/potty and we had messes more often than not.
With our second son, we decided we would let him tell us when he wanted to be free of diapers and use the toilet/potty. It worked wonders to let him tell us "I need to go, help me remove my diaper so I can use the toilet/potty." not in those exact terms obviously. We tried to always ask him if he wanted to use the toilet when we noticed him needing to go and if he said no, we wouldn't bother getting him to the toilet but we would explain to him what would be needed if he didn't use it (diaper change, clean up, etc).
So, when you suspect your baby needing to go to the toilet, ask her if she wants to use the toilet instead of doing it in her diaper. If she says no, explain why the toilet is easier/faster and if she still refuses, don't force it. Rinse and repeat till she says yes and when she does, congratulate her of her choice and explain again why it is faster/easier and cleaner to use the toilet. Always congratulate her when she decides to use the toilet, positive feedback works very well. Having your baby understand that it is easier, faster and cleaner to use the toilet will make her want to do it on her own, even more if that makes you happy. Also, ask her if she wants to keep the diaper and explain to her that if she does not want it anymore, she needs to use the toilet. Again, don't force her out of diapers if she doesn't want to. Our son didn't want to remove it even after using the toilet a few times, it took a little while before he felt confident enough to tell us he didn't want a diaper and wanted to wear panties like his brother.
We'll use that again with our currently 16 months daughter as it is a lot less stressful and much much easier from our experience.