Family member bought a white dress to wear at my wedding

So I recently went dress shopping with my mother and grandmother to pick their dresses for my wedding. My grandmother tried on a white dress and loved it. This was the second dress she tried on and choose to not even try any of the others she picked out. Before asking me if it was okay that she wear a white dress, she said I’m getting this one and sat down. My sister pointed out to her that maybe this was not an appropriate choice and it was not until then that she asked my opinion. I told her that I didn’t mind her wearing white as long as she felt comfortable, so she bought the dress. Fast forward a few days and she asks me to take a picture of her dress because she forgot to. She brought her dress out in front of the whole family during the holiday weekend and total chaos ensued. Long story short my family got in a fight about how that was not appropriate for my grandmother to choose to wear a white dress. She was very upset and offended that everyone came at her. Now I personally don’t mind but I do feel a little odd that she just assumed it was ok and was offended by comments made by our family members. Am I under reacting or is my family over reacting?
By the way my grandmother is young and of sound mind so she was well aware of what she was doing.