Mariam says she wears the niqab, or full-length Islamic veil, by "personal choice" and for "religious conviction". From today, if she leaves her home in the Paris suburbs she will have to expose her face in public for the first time in five years.
"I have decided to obey the law but to leave home as little as possible," the 32-year-old said. "I accept that the law of France is the law, even though I think that it is foolish and wrong to force me to go against my beliefs."
Most French Muslim women who wear the full-face veil are expected to bow, like Mariam, to the so-called "burka ban" which takes effect today.
But pockets of fierce opposition remain. On Saturday, police arrested 61 people who tried to hold an unauthorised demonstration against the ban in Paris. They included 20 women wearing the niqab – the Salafist or Saudi full-length veil with only a narrow eye opening.
Among those protesting or hoping to protest were a handful of Islamist extremists from Britain and Belgium, including Anjem Choudary, once a member of the banned group Islam4UK and a follower of the extremist preacher, Omar Bakri. Mr Choudary was arrested at the French border.
Their involvement was a political windfall for President Nicolas Sarkozy and a source of frustration for moderate Muslim leaders in France who have been trying to distance themselves both from the burka and the burka ban.
The law against "concealing the face in a public space", passed by the French parliament last October, was initially supported on both the left and right of French politics. It was seen as a defence of women's rights and a re-statement of the liberal and secular traditions of French society. It was also seen as a way of countering the advance of radical and intolerant strains of Islam.
Left-wing parliamentarians mostly abstained in the end because they did not want to be associated with what they saw as a wider drift by President Sarkozy towards alleged Islam-baitings.
Whatever its origins, the veil ban is in danger of being jumbled with other government initiatives such as a debate last week on "Islam and the secular state" and a series of provocative remarks on Islam by the new interior minister, Claude Guéant, Mr Sarkozy's former chief of staff, who recently suggested the growing number of Muslims in France could cause a problem.
Nonetheless, all sides except the hardline Islamists have agreed to try to take the heat out of the ban and to ensure that it takes effect with as little confrontation as possible. Last month the government instructed police not to force, or order, women to remove their face coverings in public or even in police stations. If a woman refuses to comply with the law, her name should be forwarded to the state prosecutor.
Moderate Muslim leaders cooperated with the government in drawing up the guidelines and many of the tiny number of fully-veiled women in France have already started complying with the law in advance of today's deadline.
Mariam said she had been insulted on the street on several occasions by people who believed that the ban had already taken effect. She said that, as a result of similar abuse, she knew of several women who had already started to leave their homes unveiled.
Mariam, married with three children, is a French citizen whose Tunisian-born parents never approved of her decision to wear a full-length veil. Young and French-born from a moderate Muslim family, she exactly fits the profile of the very small number of fully-veiled women in France.
According to a French internal intelligence service investigation last year, 1,900 women wear the niqab in France. None actually wear the burka, the all-encompassing and more restrictive garment popular in Afghanistan.
Since there are an estimated two million adult Muslim women in France, niqab wearers amount to roughly one in 1,000 or 0.1 per cent. The typical fully- veiled woman is young, French-born and a recent convert to a purist or radical form of Islam. Half are under 30 and the vast majority under 40. Two- thirds are French born. One in four is a white French woman who converted to Islam before or after she got married. Such a woman, Aya, formerly Hélène, told the news agency AFP last week that she had converted at the age of 14. She had begun wearing the niqab in 2005 "after I learned that this was the kind of veil worn by the wives of the prophet".
"But I don't wear it all the time," she said. "Because it is a very difficult thing to wear [when you leave Paris] and go to the provinces."
Moderate Muslim leaders in France reject the suggestion that the niqab is recommended by the Koran or associated with the wives of the prophet. Some have supported the ban; others fear that, by appearing to attack Islam itself, the ban will harden attitudes and persuade even more young Muslims to follow radical preachers.
The law which takes effect today does not mention the niqab or burka by name. It proscribes all facial coverings, except for reasons of health or safety (such as motor cycle helmets or welding masks). It also allows exceptions for carnivals and for "Father Christmases". Any woman who persists in wearing a facial veil can be fined €150 (£133) for a first offence. There are stiffer punishments – rising to a €30,000 fine and one year in jail – for anyone who forces a woman to wear a veil "by threats or violence".