it's great that she's already recognizing when she needs to go! one of the other keys - can she put on and take off her pants yet? if she can, then she's good to go. if not, you may want to start off a bit slower....go ahead and introduce the pull-ups, but dont force the issue.
asking her if she needs to go is great advice. the other thing you can do is start making notes (mental or i actually keep a log) of when she's eaten/drunk, and how long it is before her diapers wet. if you do this for a few days, you'll find that she's usually going within in a certain amount of time. the time is different for every child. once you have that info, introduce her to the potty a few minutes prior to that.
remember at this stage, she's telling you when it's happening....not BEFORE it happens.
