LD, I'm glad you had such a good relationship with "Uncle Bobby", it sounds like you both cherished each other's company. However, I have to disagree with you on your use of language. Forget "political correctness", as I say above, these words are archaic and incorrect, not to mention cruel. Imbecile, idiot and moron used to be "classifications" used by the medical profession to label people with intellectual disabilities, would it be okay to have these words used to describe someone you love? I doubt it. As I expressed in another thread, words have the power to evoke both positive and negative images and ideas. It is important to understand what is behind the language we use and WHY some words are offensive, not just that they are.
You said "it won't make a difference at all. She will still be a "beautiful mentally retarded person" who will grow up to give much love to those who love her". I appreciate your sentiment but with respect, I think it is misplaced. What anyone looks like SHOULD not make a difference, but we all know it does. What WILL make a difference to this girl will be the attitudes of the people she encounters in her, the respect she receives as a human being, and most importantly the opportunities she may or may not have to grow, reach her full potential and achieve her goals and dreams. All of these things are inextricably connected.
Having a disability - whether physical, intellectual or otherwise, need not prevent us from reaching our full potential, unfortunately the attitudes of others can and do.
IMO (and experience)