She was taken into custody after holding up a photo of the Dalai Lama while walking down a road in the county seat.
Guo Feixiong is subject to constant verbal abuse and sleep deprivation by cell-mates, activists say.
Villagers risk punishment for show of loyalty to the exiled spiritual leader reviled by communist authorities.
Lu Yuyu and Li Tingyu have been formally arrested on public order charges, rights groups and lawyers say.
Thousands of villagers continue to protest amid an information blackout by local authorities.
Activists had hoped to highlight grievances such as land grabs at the summit venue, but are now under round-the-clock surveillance.
Following a rare admission that the army killed five villagers in Shan state, Amnesty International urges national leaders to ensure victims of military abuses receive justice.
Uyghur herder: “We are forced to move, our village and heritage is going to vanish without a trace.”