Mtetwa was arrested in March while representing Prime Minister Morgan Tsvangirai's aides during a raid at their offices.
A police officer testified that Mtetwa insulted detectives searching the premier's staff offices by calling them "Mugabe's dogs" and saying they were a confused lot.
Mtetwa's lawyer Harrison Nkomo said the charges were "dreamt up" by the police and the prosecution to build a case against the lawyer, who has represented many political and rights activists.
"If anyone was obstructed, it was the accused who was hindered in the discharge of her duty as a legal practitioner," Nkomo said.
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According to Nkomo, the police did not show her a warrant to search her clients' offices, denying that she obstructed the police.
Mtetwa claims that in an effort to beef up the case, police have approached her former husband to dig up "dirt" about her past.
The Swaziland-born lawyer further alleges that secret police also went to the immigration department to check if her papers were in order.
Mtetwa's arrest and detention sparked international condemnation, and the Law Society of Zimbabwe said it was an effort to "intimidate lawyers" in the southern African nation.