Debbie Vincent is accused of conspiring to blackmail with members of the Stop Huntingdon Animal Cruelty (Shac) group against Cambridge-based Huntingdon Life Sciences (HLS) during a 10-year period.
Michael Bowes QC, prosecuting, said that the protests, which targeted suppliers and customers of HLS, included accusing staff members falsely of being paedophiles, and sending incendiary devices and hoax bombs.
Mr Bowes said that Ms Vincent worked alongside the masterminds behind Shac, Greg and Natasha Avery, at their headquarters near Hook, Hampshire.
The pair were among seven defendants jailed for a total of 50 years in 2009 for their part in the conspiracy.
Ms Vincent, of Croydon, south London, denies the charge of conspiracy to commit blackmail.
The trial continues.