Cosse, who quit the EELV Green Party because its leaders opposed her taking the housing portfolio, told the Journal du Dimanche newspaper that she was "shocked" by the way the row over the burkini has been blown out of all proportion.
"A ridiculous question has become an obsessional national debate," she commented, although she said that "as a woman" she was disturbed by the garment.
She also accused mayors who have said they will not scrap their local bans following the Council of State's ruling against one in a test case on Friday of being "pyromaniacs", motivated by electoral considerations.
"Something dangerous is happening" in France after the Paris and Nice terror attacks, she warned, where people are being attacked "simply because of their religion or skin colour" and accused right-wing politicians like former president Nicolas Sarkozy of exploiting the question ahead of the Republicans party's primaries for next year's presidential election candidate.
Her stance puts her at odds with Valls, who backed the mayors who issued bans and declared the debate on the burkini should continue after the Council of State ruling.
Two other women ministers, Najat Vallaud-Belkacem and Marisol Touraine, have also differed with Valls on the question.
Cosse said that she had "not had the opportunity" to discuss it with Valls, adding that he should be given credit for speaking out against discrimination "on several occasions".
The minister also told the paper that she "would not hesitate to take over public property" to house migrants, if necessary, talking of an "unprecedented migratory phenomenon" facing France today.
Some 70 migrants are arriving in Paris every day at the moment, she said, and 15,000 people have been housed in the Ile de France region around the capital in the last year, half of them over the last two months.
The government is to set up a new centre with Paris city council, she added, but said that "some others" are not doing their share to tackle the challenge.