She was giving evidence at the Old Bailey, London, for an eighth day, where she is accused of conspiring to hack phones and other charges.
Mrs Brooks, 45, who denies the charges, spoke of the stress of finding herself the "central figure" when the Guardian broke what she called the "horrific" story in July 2011.
Under questioning from her lawyer, Jonathan Laidlaw QC, Mrs Brooks - who was by this time chief executive of News International - told jurors she and her colleagues were horrified by the allegations and desperately tried to find out if they were true.
She said that as the story made headlines around the world, "we were completely at a loss and all over the place really, trying to find out what was true and what wasn't".
Jurors heard a text sent from Mr Blair to Mrs Brooks on July 5 read: "Let me know if there's anything I can help you with. Thinking of you. I've been through things like this."
Mrs Brooks replied: "Thank you, I know what's it's like. GB (Gordon Brown) pals getting their own back. Rupert and James (Murdoch) have been brilliant.
"Hopefully even in this climate the truth will out."
The court heard the "storm" led to the decision being made to close the Sunday newspaper, and the final edition was published just days later, on July 10.
Mrs Brooks went on to resign on July 15.
She spoke of her shock when police ordered her to "immediately" leave the News International offices that morning and said she was further surprised when she was arrested two days later.
The trial continues.