A woman is facing up to four years in jail for allegedly posting photographs and the mobile phone number of a teenage girl on a website and suggesting the girl wanted sex.

Elizabeth Thrasher, 40, posted the 17-year-old's details in the Casual Encounters section of Craigslist, prosecutors said as the first case to be prosecuted under a new cyber-bullying law got under way.

The girl, who is the daughter of the girlfriend of Ms Thrasher's ex-husband, was bombarded with calls, lewd messages and pornographic photos.

Prosecutors said that Ms Thrasher had been bickering on the social network website MySpace with her ex-husband's girlfriend and the girlfriend's daughter sent Ms Thrasher a MySpace message telling her to grow up.

"Who started what is up for debate," Jack Banas, a prosecutor in St Charles County, Missouri, said.

In revenge Ms Thrasher created a posting on Craigslist – whose Casual Encounters section warns that the pages may feature adult content – that included the girl's picture, the name of her employer, her e-mail address and mobile phone number.

Ms Thrasher was arrested and then freed on a $10,000 (£6,000) bond, but a judge barred her from having a computer or internet access at home. If convicted, she could face up to four years in a state prison, or up to a year in a county jail, and a $5,000 fine.

Ms Thrasher, who has two children, is the first person charged with felony harassment under a law passed in Missouri last year after the suicide of 13-year-old Megan Meier. Megan killed herself after a teenage boy called "Josh", with whom she had flirted on MySpace, made hurtful comments. "Josh" was in fact an adult neighbour.

A jury in California, where MySpace has its servers, found the neighbour, Lori Drew, guilty of three federal charges, but a judge overturned the verdicts and said he would acquit her. His decision has not been finalised.

Ms Thrasher's attorney, Michael Kielty, said that what his client was accused of doing was no different from someone posting a number on a bathroom wall, telling people to "call Jane Doe for a good time".

"It may be in poor taste. It may be inappropriate, but it's not criminal behaviour," he said, adding that the state law had been poorly written.

Megan's mother, Tina Meier, who campaigns against cyber bullying, said that the law should be "used to the fullest extent".

"This is not a joke," she said. "There have been too many people who have taken their own lives, too many people and their families getting hurt by this."