"I've never seen anything like it," Ivens told The Associated Press in a phone interview Wednesday. "It's definitely the most bizarre shoot I've ever been on."
Representatives for Spears had offered an exclusive interview that was intended as career comeback for the 25-year-old pop singer, Ivens said.
"What actually transpired on the day was a shock to us and left me and the whole crew feeling quite shocked and sad, really," she said.
During the shoot, Spears wiped grease on a designer dress, treating it like "a napkin," said Ivens, and sat back and watched as her Yorkshire terrier puppy defecated on a $6,700 (EUR4,900) designer gown.
"I wasn't in the room but I was there to hear the upset shrieks of the stylist," Ivens said. "Her assistant dealt with it in the end, after being asked to take care of it. They had to be asked to clear it up."
Spears took frequent trips to the bathroom - leaving the door open - and complained that the high-end clothing put together for the July 19 shoot was not sexy, short or tight enough, the magazine said.
After about three hours, Spears bolted before the shoot was over, walking away with more than $14,000 (EUR10,200) of borrowed apparel, Ivens said.
OK! publicist Brian Strong said the magazine did not publish the photos in its latest issue because they "weren't up to standard."
A representative at Jive Records, Spears' record label, did not immediately return a phone call and e-mail seeking comment Wednesday.
"She needs to have a really strong team to advise her what to do, what not to do," Ivens said. "And then, if she gets that, I'm sure she can pull it around. It's all there. She's got talent. She just needs to get her priorities straight, I think."