"I didn't know at all, I had to change everything," she said. "I've had so much support but the preparation for this was four years and this last year ... it wasn't part of the plan."
Hewitt linked with experienced coach Chris Pilone in May and believed she was in good shape coming to Rio.
However, she said there was no way her preparation was what it might have been.
"Changes are good but when it's not like what's supposed to happen, then it's difficult.
I've got mixed feelings. I'm happy I was able to race here and that I actually made it."
The 34-year-old finished ahead of 13th-placed compatriot Nicky Samuels in a race won by Gwen Jorgensen of the United States.
Both Kiwis were in a group of 18 that came off the bike leg together but Jorgensen and Switzerland's Nicola Spirig Hug cleared out from the rest of the field on the 10km run.
The 30-year-old Jorgensen, the reigning ITU champion, put distance between herself and the defending champion on the last of the four 2.5km laps at Copacabana.
Spirig Hug held on to silver while Britain's Vicky Holland outsprinted team-mate Non Stanford to win bronze.
Hewitt said the leading peloton was twice as big as she and Samuels wanted on a tough, hilly course. The large group suited superior runners such as Jorgensen.
An unwell Hewitt started the run conservatively and dropped as low as ninth but felt better in the last of four laps, finishing one minute 59 seconds behind Jorgensen.
A five-time world series overall medallist, the Olympic dais has been elusive for Hewitt.
She was eighth in Beijing and sixth in London.
Samuels, 33, was pleased with a "solid" effort, particularly after sitting out 2015 with knee and hip injuries.
Both Kiwis will contest the two remaining world series races, in Canada and Mexico, this year.
-NZN
