Lol, i should have phrased it better.
What i meant was that because i had forgotten where the series was set (most likely America... they have some stereotypical "British" guy in the series), she sounded "normal" with regards to the locale (i.e. she didn't sound like she was Irish).
As for why it was off-putting... it's not specifically that it's Irish, more so the fact that i was so unaware to the fact that she wasn't. I'm not really sure i can explain it, just that both me and my flatmate thought she'd lost some of the initial attractiveness after she started speaking with an Irish accent.