OK! Exclusive: Inside Britney's Diva-Licious Birthday

Is Britney Spears starting to crack under the pressure?

Following a pair of performances on Good Morning America on Tuesday morning, the superstar birthday girl was back to her some of her old diva tricks as she arrived more than an hour late to shoot her pre-taped segment for the annual Christmas tree lighting ceremony at NYC's Rockefeller Center.

"You have no idea how many times Britney has changed things on us, at least 14 times since I got here on Thursday," a source connected to the TV special tells OK!. "It is Britney Spears and she can do that because they want her to boost ratings, but no one is happy putting up with this. I probably shouldn't say this, but guys on the crew were making bets about whether she would show up at all."

One eyewitness tells OK! that Britney had been scheduled to appear live on Wednesday night's broadcast, but that plan was ultimately scrapped in favor of a pre-taped "message."

"She was originally supposed to perform live and then she wanted to pre-tape her performance instead," the source says. "Then she didn't want to do that. She keeps changing her mind and now she's not performing at all."

CLICK HERE for OK!'s Ultimate Britney Gallery!

Following her delayed appearance at Rockefeller Plaza, where it took multiple takes for Britney to record her "Happy Holidays" message, it was off to the Rainbow Room high atop 30 Rock.

Looking elegant in a sexy black dress with her hair swept up, Brit and an entourage of 11, including her manager Larry Rudolph, her assistant, security guards, parents Jamie and Lynne Spears and her boys Sean Preston and Jayden James, sat at a table overlooking Manhattan.

An eyewitness tells OK! that the group dined on carpaccio for appetizers and later ate salad, risotto and had a choice of chicken or beef from a pre-set menu.

At one point, Jayden started crying and Britney pulled the toddler on to her lap.

"Jayden kept screaming 'Daddy', it was so sad," the eyewitness tells OK!. "She asked for a high chair. Jayden was throwing a tantrum so Britney picked him up and walked outside. As she did, she literally snapped her fingers at her security guards who immediately got up and followed her outside."

Nanny to the rescue! After failed attempts to calm her son down, Brit finally handed him off to a nanny who quickly left the restaurant.

In the meantime, Britney's other son, Sean Preston, was having a great old time sitting happily next to his grandma, Lynne. Towards the end of the night, servers brought out a giant triple layer chocolate cake with berries and everyone sang "Happy Birthday" to Britney. The table then enjoyed a round of celebratory bellinis.

"Britney ate only the smallest bite of her birthday cake!" the eyewitness tells OK!. "She must be on a strict diet."

CLICK HERE for OK!'s Ultimate Britney Gallery!

Brit-Brit finished off her big day at NYC hotspot Tenjune, where the singer and her party of around 50 people, including Lance Bass, Jeremy Piven and Russell Simmons, took over the entire back room for a private party.

But unlike most celeb birthday bashes, where top-shelf booze flows like water, there were no bottles of alcohol permitted at the tables — only non-alcoholic drinks like Red Bull — though guests could order cocktails.