Both Vanessa Way and Jody Hartstone are based in the UK with Way under the guidance of leading dressage exponent Carl Hester.
The New Zealand eventing team is set to be named in early July.
"The Olympic selection criteria agreed between Equestrian Sports New Zealand and the New Zealand Olympic Committee was tough," NZOC secretary general Kereyn Smith said. "We're delighted she has met the challenge and we look forward to seeing her in London."
Hill will compete at the national dressage championships and the 2012 New Zealand Horse of the Year in March before heading to Germany where she will base with her trainer Andreas Mueller.
"Those two events will give her big atmospheres equal to any she is likely to face offshore and both are world-class competitions," ESNZ high performance director Sarah Harris said.
"We set the bar high for all our riders hoping to make selection for London, and Louisa has just smashed those targets right out of the water.
"She is a complete professional and real competitor."
Hill qualified for London during her recent Australian campaign and Harris said she was confident Hill was on track for a 70 per cent test at the Games, which would be a New Zealand record and could place her on the cusp of a top-10 finish.
"It's still a long road to London, but I now feel it is really going to happen and we can start making final plans," Hill said.
She join 12 sailors and two slalom canoeists, Mike Dawson and Luuka Jones, as confirmed starters for the Olympics.APNZ mb lb