What the Docs May Do
Your pediatrician should take a detailed elimination history ("peeing" and "pooping" in pediatric language) with every well-child visit. The focus should be on age-appropriate behaviors and watching for early signs of withholding and constipation. A chronic and severe issue with constipation can begin to develop at this delicate time. Hard, painful, and bulky bowel movements can easily trip toddlers into a cycle of withholding and more severe constipation which might not be noticed until years down the road.
Most doctors will tell you that the most physiologic way to pee or poop is to have your feet planted firmly. Imagine trying to poop on a super-sized toilet with your legs dangling in mid air! Toddlers also feel more secure with their feet planted. So if your toddler is going to use the adult toilet, have a sturdy bench or stool in front of the toilet so she can rest her feet.
Although a bit unorthodox, our practice discourages the use of pull-on diapers, though most pediatricians do recommend Pull-Ups. They give a toddler all the benefits of big girl underwear (comfort and easy on and off), but lack the potty motivation factor that a bulky diaper automatically supplies because of the relative discomfort.
And remember, no amount of training slowness is considered abnormal (according to the Yale Child Study Center Guide to Understanding Your Child) unless your child is not potty trained by age five. So if you are stressed out by the process or your toddler is frustrated, don't hesitate to take a step back to diapers. You have plenty of time.