But shop owner John Hood dismissed her on the spot saying: "It's a good job men don't have periods."
Ms Webster took the case to an indstrial tribunal and won her battle for unfair dismissal from her pounds 105-a-week job serving behind the counter. She said: "It's a victory for women everywhere - a lot of men just don't understand what we go through every month."
The tribunal was told Ms Webster had taken off just a "handful of days" in three years working behind the counter at the Food Glorious Food takeaway in Rumney, Cardiff. She was dismissed over the phone after calling in with PMT and stomach cramps.
After her courtroom victory, she said: "I suffer really badly from PMT every three months or so. I get really irritable as well as getting terrible back and stomach pains. I just have to lie down and keep still until I feel better."I felt I had to go through with this case to make a stand for other women."
The Cardiff tribunal awarded Ms Webster pounds 442 in compensation after unanimously ruling she was unfairly sacked.
After losing the case, Mr Hood said: "I admit I got it wrong. I did not handle the situation the right way and it's fair enough that Sarah won. But I've been told the amount she was awarded is the lowest possible and I think that's right."
n A nurse has won a pounds 50,000 settlement after bringing a claim of racial discrimination against a National Health Service trust, the Commission for Racial Equality said yesterday. Nargis Firdous, who was a ward manager for the Bethlem and Maudsley NHS Trust in south-east London with more than 14 years' experience as a nurse, claimed a line manager carried out a sustained campaign to remove her from her post.