It was my understanding that, in traditional Western weddings, if the bride were to become unavailable on the day of her wedding then the groom was expected to wed the maid of honor or the next available bridesmaid, thus precluding married women from serving as bridesmaids.
In Western tradition, there are several positions that a woman can take in the party of the bride: she can be a bridesmaid which means she is any of the attendants, a maid of honor if she is the principal unmarried bridesmaid with more duties, or matron of honor if she is the principal bridesmaid who is married. A maid (or matron) of honor is different from a bridesmaid:
In North America, a wedding party might include several bridesmaids, but the maid of honor is the title and position held by the bride's chief attendant, typically her closest friend or sister.
Times certainly have changed, and the tradition of bridesmaids needing to be unmarried no longer holds. This Q&A on The Knot said:
The idea that a bride needs to be surrounded by unmarried women is ancient history, and unless all your closest friends do happen to be unwed, it might as well stay that way. There's no reason you can't ask a married friend to be a maid. You can refer to her as a bridesmaid in your programs, and everywhere else too -- no need for a bridesmatron title. Think of it this way: Being a bridesmaid is more like being a "Ms." than a "Miss."
The definition of bridesmaid is:
a woman who is an attendant of a bride
By definition, a bridesmaid does not have to be unmarried. Further, in common practice, a bridesmaid need not be unmarried.
After simchona clarified what exactly was the problem, I looked it up, in Bride's forum, and someone asked a similar question:
Is there a special name for a bridesmaid that is married? I am having my older married sister as my Matron of Honor and my unmarried younger sister as my Maid of honor. One of the bridesmaids is married ... can I still call her a bridesmaid in the program?
Three of the answers all agreed on one thing:
a married bridesmaid is still a bridesmaid-
the only time it changes is when the maid of honor is married- then it becomes matron of honor.