Brides arrive first thing to prepare for their big day, before meeting their groom outside and going to the ceremony, she says, sorting through a rail of Chinese-made gowns.
Mother-of-three Gloria Mutero, 45, is won over.
"To buy from somewhere is very expensive," she said, adding that renting a dress from a shop in town cost $150.
But she said she was unwilling to spend a lot on something she would only wear for "three (or) four hours".
"I like this one," she says, looking at a dress on display in the caravan. It's "decent" and "cheap," she adds.
"Maybe if I negotiate, they are going to give it to me for $50," she says, looking towards Siwardi and her assistants.
The white-roofed caravan is one of three offering similar services outside the court.
Siwardi, a widow and former teacher with a broad smile, says her profession has at times turned her into a confidante—particularly for brides who "rush" into things.
"Some call maybe after a month and say: 'I want to divorce'," she says with a giggle.