It sounds to me like too much negative attention is surrounding her bathroom habits & she's gotten to the point of where she just wants to go and be left alone and use the restroom in a corner.
I think consistant postive attention & rewards would go alot further in reinforcing her toilet training. Perhaps you could make up her own personal calender & buy some stickers that she likes (Barbie, Dora, etc) & reward her with stickers for everytime she makes it to the potty. Tell her if she gets X amount per day & a total of X amount per week at the end of the week she can have a reward (perhaps her favorite dessert or a family bike ride). Be sure to start out with a small amount and work her up to a larger amount of dry-time stickers.
Another suggestion I have would be to not MAKE her sit on the toilet for long periods of time; that isn't working anyway. Ask her to join you when you use the restroom - "Mommy needs to use the restroom why don't you come try also." Bring in a cute book about toilet training & read it to her while it's her turn. Make bathroom time a positive experience - many toilet paper companies sell kids bathroom kits with everything from kid printed toilet paper, books, & hand washing materials. Go through the whole regimen with her, not just the toilet part.
As for the pull-ups, those are just to make your life easier - not hers. If you choose to forgo the pull-ups because you think she uses it as an excuse it's already been proven she'll wet anyway. I say, save yourself the headache put the pull-ups on her & positively re-enforce when they stay dry for various stints. Stickers, stickers, stickers!
I hope this helps or at least brings to mind some other ideas. I wish both you & her the very best.