from what i understand, sikh women stopped wearing turbans because the mughals used to pay people to bring in a sikh's head. women in turbans were also decapitated and their heads brought in, disguised as the heads of boys. so the women stopped wearing dastaar in order to protect themselves from this bounty. after a while, the custom of women in dastaar just faded away.
As far as my knowledge of sikh history is concerned there is no reliable evidence that large number of sikh women wore turban