FWIW, I agree with Carolyn that this seems more motivated by dislike for Linda than any real concern for the child. I also agree that nicknaming from relatives who love you is primarily a sign of affection; if the kiddo doesn't want to be called a nickname and complains and Linda keeps doing it, then Linda is in the wrong.

It reminds me of the way my mother gnashed her teeth and wailed when I decided to keep my maiden name. "But your children will be so confused! Everyone will think you're divorced! Or that your husband is dead!" None of these things have happened, not even once. LOL