"I was treated like a criminal," Kashif said in a telephone interview. "I am confused what to wear. The trousers were an issue. My skirt was beneath the knee. What more can I do? I am Christian. My tribe and my customs permit me to dress like this."
Human rights lawyer Azhari al-Haj said a legal team plans to sue the authorities for procedural mistakes and to exonerate Kashif.
Kashif's ordeal follows the high profile case of Lubna Hussein, a female journalist who was sentenced to 40 lashes for wearing trousers deemed indecent. Hussein's sentence was reduced to a fine, and she is now lobbying to change the morality laws.
Sudan's indecency law allows flogging as a punishment. Human rights campaigners say the law is vaguely defined and arbitrarily enforced -- and often incorrectly applied to non-Muslims such as south Sudanese Christians living in the capital.
Under a 2005 peace deal that ended a 20-year civil war between the Muslim north and the Christian and animist south, laws -- including the indecency law -- are supposed to be reviewed to respect human rights and freedom of expression.
Sudan's government implements a conservative version of Islamic law in the north. Public order police enforce the laws, banning alcohol, breaking up parties and preventing men and women from mingling in public.
In northern Sudan, many women wear traditional flowing robes that also cover their hair, but it is also not uncommon for women to wear trousers, even though conservatives consider it immodest.
Kashif, a high-school student, said she was heading to the local market in a Khartoum suburb to buy vegetables when she noticed a man following her. When she confronted him, she said he grabbed her by the hand and led her to a police station, where he charged her with wearing indecent clothes.
Kashif said she was lashed on her back, hands and legs.
"I came home and slept for a whole day. When my family found out, we all cried," she said.
Al-Haj, the human rights lawyer, said his group will protest that authorities gave Kashif the maximum sentence and ignored that she was a minor and a Christian.
"The whole thing from her arrest to her flogging didn't take one hour and half. This is unprecedented," he said. "We want to question the police officers and the judge, to exonerate Silva and to campaign against these laws."
Amal Habbani, a women's rights activist and columnist, said cases of flogging women for wearing clothes deemed indecent are backlogging the Sudanese legal system.
All that's needed to prosecute a woman for a dress violation is a complaint, and there are many thousands filed each year, she said.
"Most of these (violators) receive quick trials and sentences and they don't speak about it," Habbani said. "This is repression of a whole society through its women."