My mother has given my daughter a nickname I really dislike because she doesn't like the name we picked. Help?

I want to name my daughter Aerin Michelle. My mother absolutely hates it and is now insisting that we call her something "cuter". When I wouldn't budge on it she immediately dubbed my daughter "Shelly". My fiance and I both are horrified. That's NOT the name we picked and we feel she doesn't have to right to undermine us like that. Am I hormonal or is she really stepping on toes here?