Of course they can. If we had more female leaders in the world I think the world might be a less volatile place, and they are just as, if not more so, capable as men in a leadership role. Look at how women manage a household, how they project manage in the business world, even how many have led countries.
I think it is a shame that Hisb ut-Tahrir has categorically said no to having a female khalifah in its draft consitution, considering they are perhaps the most popular group advocating an Islamic State.