Neill or Ó Neill is an Irish surname, (hinting VERY slightly that she would be more likely to be republican than unionist, especially since she wears GAA shorts a lot which are official irish national sport gear for hurling and gaelic football, but she prob just wears them because she doesn't give a shite and they look cool, which is actually nice to see).
HOWEVER someone above mentioned her father's name which definitely is more of a British name, but that doesn't really mean much either because people can have names for many reasons.
Most importantly, none of this really matters because Olivia definitely doesn't involve herself in politics and why would she!
Protestants and Catholic culture/tension in NI is a very difficult and complex subject, if you want to know more search "The Troubles in Northern Ireland"