Meera was never married, she was single and living with her sister when she met the Virani family, then she fell in love with Mihir. Since Mihir she is only waiting for him to marry her, so she can not have children.
Maybe Meera kidnapped Karan and Nandani's child who is a daughter and made her negative and that daughter marries Laksh, but that would he cousin's marrying which is wrong.
Or maybe Meera's sister had a daughter and Meera is using her to take revenge, because Meera cannot have a daughter!!!