When Jennie Linn McCormack walks the streets of Pocatello, the town in southern Idaho where she was born, raised, and still lives, she attempts to disguise her face by covering it with a thick woollen scarf.

It doesn't really work. In the supermarket, people stop and point. At fast-food outlets, they hiss "it's her"! In the local church, that supposed bastion of forgiveness, fire-and-brimstone preachers devote entire sermons to accusing her of mortal sin.

Ms McCormack never wanted to be notorious. A 33-year-old single mother, she has for years devoted herself to raising three children on $250-a-month (£160) in child support, plus cash from a part-time job at the local dry cleaners.

Then, last autumn, came the controversy that would change her life. It began when she learned she was pregnant and decided to self-administer a termination. The ensuing events have placed her front and centre of the next great legal showdown in America's endlessly divisive abortion debate.

In Pocatello, that's not a great place to be. This deeply conservative town of about 55,000 residents, with a railroad and a small university campus, is dominated by its churches. Some are Mormon, others fundamentalist Christian, all of them vehemently anti-abortion.

"I feel like my life is over," Ms McCormack says. "I now stay home all the time. I have no friends. I can't work. I don't want to take my kids out in public. People can be really mean about what has happened."

When Ms McCormack fell pregnant, she was unmarried, alone, and living in a tiny apartment with three children. The potential father of her fourth was no longer on the scene; in any case, he was penniless. It would, she concluded, be barely possible to survive with another baby.

With this in mind, she decided to have a termination. But in Pocatello, this is not easy. The nearest abortion clinic is in Salt Lake City, almost three hours' drive away. She had no car, no one to care for her youngest, who is two, and since the local law mandates a waiting period for abortions, she would have been obliged to make two round-trips.

After transport, there were medical expenses. With no savings and only a tiny income, Ms McCormack was concerned about financing a procedure that could set her back thousands of dollars. Alone, and without a computer, she was unable to research alternatives. And that's when someone told her about a pill called RU-486.

Ms McCormack is legally barred from discussing what happened next. But she told police, when later arrested, that she had telephoned her sister, who lives in Mississippi, and asked her to purchase the drug, which induces a miscarriage, over the internet. She allegedly took the pill, which cost a little over $200, on the day it arrived by post. Things immediately went wrong. RU-486 is licensed for ending early term pregnancies. But Ms McCormack's was more advanced than she thought, perhaps as much as 21 weeks. The size of the foetus terrified her. So did the blood. In a panic, she placed it in a cardboard box on her porch, and called a friend. That friend telephoned the police.

So began a legal saga that is now winding its way upwards through the justice system and, should it reach the Supreme Court, may see Ms McCormack's name preserved alongside that of Jane Roe, the plaintiff in the Roe vs Wade lawsuit that in 1973 established the constitutional right of US women to an abortion.

Under Roe vs Wade, terminations are legal in the US until the foetus is "viable", or able to survive outside the womb, a point at around 23 weeks. But Idaho has a law, never before enforced, which bans women from carrying out their own abortions. It was under this, Idaho Code Section 18-606, that Ms McCormack was arrested and prosecuted.

In court last summer, the case was dismissed, due to lack of evidence. "The US has a law called corpus delecti which posits that you can't only convict someone on the basis of a confession. There has to be other evidence," Ms McCormack's lawyer, Richard Hearn, says. "In Jennie's case, there was none. The autopsy found no medicine in the foetus. Prosecutors had no computer record of the pill being brought, no packaging or boxes in which the drugs came."

Despite the ruling, it still remains possible for Ms McCormack to be charged again with a crime that could carry five years in prison. Mr Hearn has filed a lawsuit claiming that Idaho's law (similar to ones on the statute books of six other conservative states) is unconstitutional and should be overturned.

"I have two aims," Mr Hearn says. "The first is to prevent Jennie from being prosecuted and to give her a right not to live in fear. The second is to set a precedent. If Idaho cannot prosecute a woman for taking RU486, then women in the USA will be able to legally have access to abortion drugs from their computer. That would be revolutionary." The lawsuit is currently before the Ninth Circuit Court of Appeals, one rung beneath the Supreme Court. It carries far-reaching implications. Although 35 per cent of American women have abortions at some stage, many face severe upheaval to access them, since 98 per cent of rural counties do not have abortion clinics. If Ms McCormack succeeds, that problem will become superfluous: US abortion law will have been updated for the internet era.

In a country still consumed by culture wars, that's a big deal. Only last week, Texas began mandating that expectant mothers be forced to see an ultrasound before undergoing a termination. And Barack Obama is still facing a relentless barrage of hostility from the religious right for attempting to ensure that employers give women health insurance that covers birth control.

At the centre of this gathering storm, Ms McCormack carries on struggling with her status as a social pariah. At first, customers at the dry cleaners where she worked started ignoring her. Then they refused to be served by her. "The more it got in the paper, the more I got dirty looks and the more people started asking for someone else to help them," she says. "Eventually, I quit."

Her relationship with her mother, a Mormon, has become severely strained. Her sister, worried about being dragged into the prosecution, has virtually stopped speaking to her.