I heard a presentation once from a LGTQ etc organization that addressed the use of expressions like "that's so gay". They quoted a study that on average, people who identify with the gay community hear a negative connotation about themselves over 20 times a day. 20 times a day they are reminded that they are unacceptable, unlovable, bad, rejected, and that who they are is a negative thing. 20 times a day.
Then I think of the word retarded and how often it is used as an insult. So while people I know would never think of P when using the word retarded, or call her that, it is sending the message that people just like her are so unlovable, unacceptable, negative etc that they are used as an insult. How many times a day, every day, will she have to hear that her disability is unacceptable? What does it do to a person to hear that? In the gay community it leads to a suicide rate that is 4 times higher than the national average.
And you bet there are kids whispering behind P's back that she is a retard. Because that's what kids do. They better not let me hear them do it though because I will rip them a new one.