But Ms Hussein's trial in the capital, Khartoum, was delayed for a month after the judge said he needed to verify if she was immune from prosecution because of her former position at the UN.
After her hearing was adjourned, Ms Hussein said the authorities wanted to delay her trial until the fuss around it went away.
Scores of women protested outside the court, some holding up banners saying "No return to the dark ages".
Then the riot police drove them away, reports the BBC's James Copnall in Sudan.
First they marched up the road, banging their batons against their plastic shields, and later they fired tear gas and charged the protesters.
One of Ms Hussein's lawyers, Manal Khawajali, complained that she was beaten up by police outside the court.
Ms Hussein was arrested in a restaurant in the capital with other women earlier this month for wearing clothing deemed "indecent" under Khartoum's Sharia law.
James Copnall, BBC News, Khartoum
In theory Khartoum is governed by a relatively strict interpretation of Islamic law.
But the law is not meant to apply to non-Muslims, following a 2005 peace deal between the largely Muslim north and the essentially non-Muslim south.
Although Lubna Hussein says she is facing prosecution for "indecent clothing" for wearing trousers, it is not unusual to see women wearing them.
Southern girls wear tight blue jeans and no headscarves in shopping malls; Muslim women too can be seen in trousers, though usually only in the sort of cafe frequented by the elite and foreigners. From time to time southerners are arrested for producing illegal alcohol.
She said 10 of the women arrested with her, including non-Muslims, each received 10 lashes and a fine.
"Before police caught me, there are maybe 20,000 girls and women getting flogged for dress reasons," she said.
If this could happen in a restaurant in Khartoum, imagine what the situation must be for women in Darfur, Ms Hussein said.
"This is my message."
Ms Hussein and two other women asked for a lawyer, delaying their trials.
Under a 2005 peace deal between the mainly Muslim north and the largely Christian and animist south, Sharia law is not supposed to be applied to non-Muslims living in the capital.
Our correspondent says it is not that unusual to see women - both Muslim and non-Muslim - wearing trousers in the city.
Ms Hussein says she has done nothing wrong under Sharia law, but could fall foul of a paragraph in Sudanese criminal law which forbids indecent clothing.
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