The woman was handed a one-year sentence, with nine months of the term suspended, for hiding the 15-year-old boy in the boot of her car in an attempt to get him onto a cross-Channel ferry.
She was apprehended by French authorities at the northwestern port of Dieppe before they could board the vessel to Newhaven on Britain’s south coast.
The mother-of-one, who works in a London suburb as a waitress and occasional escort girl, had arrived in northern France to visit “The Jungle” migrants’ camp in Calais, which she knew well from earlier trips as a volunteer.
According to the French authorities she accepted 500 pounds (650 euros) from an Iraqi migrant at the Calais camp, who managed to get over to England and asked her to smuggle the 15-year-old across, a task she accepted for “humanitarian reasons”.
An initial court decision in November deemed her crime worthy of a year in jail.
On appeal at a court in the northeast town of Rouen that sentence was eased to three months in jail.
Including time already served in custody she should be freed on February 12.
The appeal court also banned her from entering France for five years.
Last week French justice showed more clemency to another British voluntary worker, former soldier Robert Lawrie, who was only fined 1,000 euros for attempting to take a four-year-old Afghan girl out of the Calais camp in order to drive her to Britain.
Unlike his compatriot he received no money and his act was deemed to be unpremeditated.
On a visit to Paris on Monday Lawrie urged people to understand the desperation of the migrants fleeing war and misery as they languish in a camp with some 4,000 inhabitants, mainly from Syria, Afghanistan and Iraq but also Sudan and Eritrea.
“You can’t help everyone. But everyone can help someone”, said Lawrie, a father-of-four from northern England who has visited The Jungle several times to build shelters for the migrants.