Please help me....the "retarded" word really offends me...?

and a woman I work with continually uses it even though I've explained (compassionately the first couple of times, and quite irritated the last couple of times) that it would probably hurt my daughter's feelings. My 18 year old daughter has Down Syndrome, but is high functioning, and would totally get the use of the word in that manner, and would be hurt. This woman has argued with me, that my daughter is not retarded, but mentally disabled ( not sure what the difference is? Me either). She has argued with me on two accounts about it, and continually uses it, sometimes I think she does it purposefully to get to me. Please help me....how can I make this stop...she is 45ish, and I am 42 this is absolutely crazy. I would NEVER do something to hurt someone, especially not someone who could not defend themselves as many people with retardation can not. I am very angry that you cannot call people or things, SO many other things, that I won't even bother typing, because of political correctness. However, in our society it is absolutely okay to use the word "retarded" inappropriately and hurtfully and it's still accepted. How can I stop this...please help!!!!!!!!!!!!!