By Jill Serjeant

LOS ANGELES (Reuters) - She's fired her people, fought with her mother and taken an ocean dip in her underwear. Now, a bid by pop star Britney Spears to set her bizarre record straight with a celebrity photo shoot has backfired big time.

Celebrity-friendly OK! Magazine said on Wednesday a tell-all interview and photo spread intended to relaunch the 25-year-old singer's career turned into a "heartbreaking day" of ruined designer dresses, dog poop and erratic behavior.

"What we experienced was a young girl who is desperately in need of help. And sadly she has surrounded herself with too many people who are pretending that nothing is wrong," OK! said in excerpts from its story that hits newsstands on Friday.

The interview in a Hollywood Hills home last week was requested by Spears to clear up gossip since shaving off her hair and entering rehabilitation in February, negotiating her divorce from dancer Kevin Federline and planning her music comeback.

Instead, she let her new puppy poop on a $6,700 Zac Posen gown, wiped her greasy hands on a pink silk Alisha Levine dress, took repeated bathroom breaks without closing the door and fled after four test shots still wearing more than $14,000 of OK!'s borrowed clothing, the magazine said.

To top it off, the pictures were such bad quality that OK! called them unpublishable.

"A shocked crew, which had bent over backward to accommodate Britney's demands, packed up and left with nothing but sour memories of a young lady so eager to tell the world the truth about herself," OK! said.

The OK! shoot followed weeks of unusual behavior by Spears, who became a worldwide pop phenomenon eight years ago with hits like "Oops! I Did it Again" and "Baby One More Time."

Last month, tabloid media reported a "slapfest" between Spears and her mother Lynne, whom the singer had earlier attacked in a poem in apparent retaliation for being coerced into rehab earlier this year.

Last week, Spears was pictured stripping down to her bra and see-through mesh panties to take an impromptu dip in the Pacific Ocean near Malibu. Another bizarre report last week had Spears applying to be a cocktail waitress at a Hollywood bar.

Spears fired her manager and publicist earlier this year and her attempt at a comeback in May with brief performances in local California clubs was derided for lip-syncing.

The editor-in-chief of OK!, Sarah Ivens, said in a statement the magazine had spent "a heartbreaking day with Britney Spears and witnessed first-hand an emotional cry for help that will leave you shocked and sad."