Why do you say she is too small for a regular toilet? My daughter basically self trained at 25 months. We had the potty chair in our bathroom from the time she was 18 months so she'd get used to seeing it when it was time to start. I think she used it only a handful of times here and there. Then one day a few weeks after her 2nd birthday, she said she needed to use the potty, marched into the bathroom and insisted on using the regular toilet. Granted I had to hoist her up, but no way was I allowing a 2 yr old to go potty unsupervised anyway... so that was no big deal. She was completely dry within a week, but we used pullups in public for a few months longer. She never went back to use the potty chair.
Maddie was itty bitty - 15 lbs at a year and I think only 25 at 2. She was consistently in the 5th percentile at all her dr. appts, so size definitely doesn't NEED to be a factor. I hated cleaning out that stupid potty chair. I was thrilled she decided the big toilet was the way to go!!
If the big toilet freaks her out, then they do have a collapsible potty ring you used to be able to get at Babies R Us... it folds in fourths and can easily store in a diaper bag. That is what a good friend of mine used with her daughter when we were out.