Gender Reveal

I need to vent! Gender reveals are suppose to be full of fun and excitement, right!? My cousin and best friend are planning my reveal so it only makes sense that they know the baby's sex. My MIL just called me yelling because my best friend knows before her and proceeded to throw a fit like a 5 year old. She doesn't care that my cousin knows just cares the my best friend knows... She is PLANNING the party. She kind of have to knows. None of the family members, or GRANDPARENTS KNOW. Why can't she just let it go and act like an adult? Is it wrong for me to want the gender to not only be a surprise for my husband and I but for the immediate family - grandparents - too?