Hayley appears in the family tree of the Buxton family(from Staffordshire, England... near the town of Buxton Derbyshire, where I once worked!). The link is - if it's correct - on her father's side. If it's correct, it does not, of course, rule out an Irish and Welsh connection, too!
The Origins page says that John Buxton and his family emigrated from England to Christchurch NZ between 1857 and 1862. It's fascinating to follow it through on the Family Tree pages.
The line goes: John Buxton; Joseph Buxton; Eva Buxton (who married William Wardell); Dorothy Wardell (who married Henry Menzies); Patricia Menzies (who married Aylmer Westenra); Gerald Westenra; Hayley.
I can vouch for the part that Westenra (though not a very common name here in Holland) has Dutch roots as well. I haven't really gone into this. Still, with all these multinational links, this is well and truley... HW International
The Westenra name must have been an important name in County Monaghan, Ireland, as there is still a hotel named The Westenra Arms in Monaghan Town.
The fact that the Irish songs has been passed down to Hayley from her grandmother may suggest Irish ancestry too. Also, isn't Hayley's grandmother's surname, Ireland? Surely, that proves Hayley has Irish ancestry!