Her legal team declined to give details but said prison conditions contributed to her fragile mental state.
Manning was sentenced to 14 days in solitary confinement in September for charges relating to her attempt to kill herself in July.
The transgender army private, born Bradley Manning, is serving a 35-year sentence for espionage.
She was found guilty in September by prison officials in Leavenworth, Kansas, of “conduct which threatens” after her initial suicide attempt.
She was also convicted of having “prohibited property” – the book “Hacker, Hoaxer, Whistleblower, Spy” by Gabriella Coleman.
In July, the former intelligence analyst attempted to take her own life after what lawyers said was the Army’s refusal to provide appropriate health care.
She later went on hunger strike which ended after the military agreed to provide her with gender dysphoria treatment For Tricks.
Manning sentenced to solitary confinement
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Her lawyer Chase Strangio described her treatment in a letter, quoted by the AP news agency, as “demoralizing”, adding that it was an “assault on her health and humanity”.
“She has repeatedly been punished for trying to survive and now is being repeatedly punished for trying to die,” wrote Mr. Strangio.
When she was removed from solitary confinement in October she tweeted that she was “OK” and “trying to get back in the groove of things”.
Manning was sentenced to 35 years in prison in 2013, after being found guilty of espionage for her role in leaking diplomatic cables and battlefield reports to Wikileaks, the anti-secrecy group.
The leak of more than 700,000 documents and videos was one of the largest breaches of classified material in American history.
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