Although she doesn't need an Irish passport to establish her automatic Irish citizenship, it is the only practical way of proving nationality in the absence of a national ID card. And while it is highly unlikely that the nationality rules in Ireland will change, it might be worth getting the passport now to establish her nationality formally. I'm a dual national and the only thing to remember is that you must exit a country on the same passport on which you entered. Any children she has can claim citizenship through her parents but not through her - you can only claim citizenship as an offspring if your parent was born on the island of Ireland. Claiming citizenship through an Irish-born grandparent is a bit more complicated for those born after 1 Jan 2005 - the details are on the Irish immigration website. Finally the rules apply whether the person through whom one claims nationality was born North or South of the border meaning that you could have a parent born in Belfast, say, who has always been a British citizen yet is your portal to Irish nationality. And Irish passports are cheaper than British ones!