Saretha is going to strike as soon as possible, in terms of contacting people. The FBI is immediate, as are the reporters that have come in contact with her before hand - this is as soon as she gets the information, and thus probably just prior to the attack. She doesn't agree with what the attacking Numbered are doing because she's fearful of it shooting them in the foot, but she also doesn't want to send them to their deaths - as such, she's not going to blow it to the wider media until AFTER the attack.

She won't go to police, figuring that ... effectively going over their heads with the FBI is a better move.

Otherwise, she'll talk to anyone who comes, and as prominent as she's been she'll be attempting to make her even more so.