She's there to smooth things over between Rand and Egwene, and everyone else. It is her duty to make sure that the mistakes from the Sealing in the Age of Legends do not happen again, mostly by preventing the women from abandoning Rand's plan, but possibly also because she has a better idea of what should be done, and helps Rand with the Sealing directly.

And then there is knowledge and items that she might have received, so she could really be capable of just about anything. And no doubt her appearance will have a strong effect on Rand too... And on Lan, and therefore on Malkier itself, and Nynaeve, and who knows how many other people. The important thing is that her very existence will be a catalyst for all sorts of things that occur.