Knowing what to do, and being "able" to do it are 2 different things.
In toddlers... their cognitive ability is not always coordinated. Thus, they may "want" to do something, but my not be able to, literally. This is toddler life. They are not yet, fully developed, to do it all at-will.
The main thing is praise her for trying her best. NOT expecting perfection. Nor right away. Because, there WILL be mistakes, regressions, accidents. Even a 5 year old still has pee accidents. Normal. Normal. Normal.
So, either get irked/mad at every accident/mistake... or not...
Sure pull-ups are expensive. I did NOT use pull-ups for my kids, I don't feel its necessary. I just used diapers... then when they were fully in control of their body, I used the Gerber "training pants" underwear.
Here is a link:
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3...
It has a built in padding... to wick up leakage.
Also, a child has to be able to have the motor-skills & coordination to pull-down their own clothes, to learn wiping, and then to attain nigh-time dryness.... (which this is NOT biologically attained even until 7 years old, and is normal per Pediatricians).
Potty "training" goes in steps and is a process. Sometimes months. Not days or weeks. And, again, there WILL be accidents and mistakes. Its okay. Even Kindergarten kids have accidents... and still wear night-time diapers. ALL NORMAL.
Go by your child's ability & readiness. Otherwise, they will get stressed and not want to even try.
All the best,
Susan