As evidence, they cited a tweet posted last month that read, “We are being led by a selfish & sick man,” and included a photograph of Mr. Mugabe with an illustration of a catheter. They say that Ms. O’Donovan had access to the anonymous account, with the handle @matigary, via her laptop computer, and that she used an anonymous web browser known as Onion Router.

Ms. O’Donovan’s goal, prosecutors charged, was to “replicate offline uprisings like what happened in Tunisia and Egypt” in 2011.

The @matigary account — which has accumulated a wide following, including among Zimbabwean journalists, for incisive posts about Mr. Mugabe’s government — has continued to tweet since Ms. O’Donovan’s arrest.

Obey Shava, who is representing Ms. O’Donovan and is a member of Zimbabwe Lawyers for Human Rights, said he looked forward to the start of the trial. Asked how his client was doing, Mr. Shava said, “One cannot be entirely excited as her freedom is curtailed.’’

Ms. O’Donovan’s employer, Magamba Network, which focuses on youth culture and news, describes its vision as “a democratic and just Zimbabwe.” It is funded in part by the Omidyar Network, a foundation established by Pierre Omidyar, the eBay founder.

A social media campaign started by the organization under the hashtag #FreeMartha urges Zimbabweans to call for her release, and is being spread by local and international rights groups.

“Magamba itself has been targeted for the work that we do in new media, social media,” said Samm Farai Monro, one of Magamba’s leaders and a comic known as Comrade Fatso. He speculated that the government had targeted Martha “because she is white and American and so she is an easy scapegoat.”