Healy became the first player to score a hat-trick for the province for 15 years and his international record now stands at 23 goals from 52 games.
His odds were initially halved to 50-1 yesterday, but Ladbrokes were forced to make two further cuts as money poured in from the other side of the Irish Sea.
Ladbrokes spokesman Nick Weinberg said: "This gamble is really taking shape. Healy is the man of the moment and has been backed almost to the exclusion of everyone else in the last 24 hours. Zara Philips and Andy Murray (the favourites) had better watch out!"