Is it wrong for my wife to be so possessive of her "special" nickname she has for our daughter?

My mom has been calling our daughter "pumpkin" lately. My wife is not happy about this because it's her "special" name for our daughter. I don't understand why my wife is so possessive of her "special" nickname for our daughter. It's causing problems between my wife and my mother because my wife is so upset about it.
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