I really don't know how to get her to stop,
but I would try 2 ways
Put her to her bed when she says it,
for 2 minutes or until she stops crying,
OR
Just ignoring it, which is far more difficult
because you have a natural urge to ask her to stop saying that and explain what a horrible word it is,
ONLY allow her to watch positive TV, and surround her by positive people,
Bahai's are a good group of people who are usually very positive,
OF course it is a religious group but you don't have to become bahai to be friends with the bahai's
But I think it might be just to ticket, because we teach about LOVE for everyone, All the Races, and Sexes are equal
Well here is a link, and hopefully you decide to make friends
They have great Childrens classes for FREE that will help teach her the virtues, which is what you need, BUT its a really dificult things to teach your child independently.
http://www.bahai.org/
M