The win gives Greig her third provincial title, having won in 1996, under her maiden name of Wilson, and again in 2008.
Due to a lack of entries, the event has not been played since 2010, but will now be played in conjunction with the men's matchplay championship each year.
Greig took an early lead in the final to be three up after four holes and finished strongly to clinch the title with four holes to spare.
Meanwhile, the Otago men's event will continue today with the semifinals this morning and the finals in the afternoon.
Brent McEwan (St Clair) will meet Brandon Hodgson in one semifinal, while Southland star Mathew Tautari will play Nicholas Borren (Otago) on the other side of the draw.
McEwan was tested in the first two rounds of matchplay yesterday, beating Harry Smith in the morning and John McIntee in the afternoon.
McEwan won the Ritchie Cup on Saturday as the top qualifier, with sub-par rounds of 70 and 68 for a five shot lead over Tautari and Borren.
The first round of matchplay was plagued by the incessant rain, which put the Balmacewen greens under water and caused a two hour delay in play.
Hodgson won both of his matches on the 17th green at the expense of Sean Masters (Otago) in the morning and Scott Hellier (Southland) in the afternoon.
Tautari showed he could be tough to beat as he posted convincing margins over Chris Timms (Otago) in the morning and Daniel Elder (Otago) in the afternoon.
He is an experienced and top match play golfer and was named player of the tournament at the 2011 Toro tournament in Gisborne.
Borren beat Port Chalmer's Ryan Bellamy in the morning but had a close tussle with Daniel Barnett (Queenstown) in the afternoon.
Barnett held the lead in the early stages, but Borren fought back to be square with one hole to play.
Both struck bunker problems on the final hole, Borren in a fairway bunker and Barnett in the front left greenside bunker.
Both players carded bogey fives and Borren then took the honours and a place in the semifinals after winning the first playoff hole.
There will be some good matches in the senior plate this morning, when Smith plays Masters and Timms meets Bellamy.
There was an epic battle in the masters (over 40) final. Jeremy Morgan (Otago) and Kyle Geary (Chisholm Park) required seven extra playoff holes to find a winner. With darkness falling, Morgan took the title with a par 5 on the 25th hole.
