The bio on her website says she was born in Northern Ireland, so maybe that's where they got it from. However she grew up in England - most likely her parents just happened to be living in NI when she was born. It is part of the UK, after all, not the Republic of Ireland - and there would have been lots of English living there at the time Alex was born.
One of the other members of our group is Irish by birth, but I wasn't sure about Alex.