Should she cut her hair before sister's wedding or not?

My younger sister, Jo, is getting married May 1st, and my older sister Lynn and I are bridesmaids, along with two of Jo's close friends. Lynn has a 4 month old daughter. Lynn recently decided that she wants to cut her hair super short (think Ellen DeGeneres or shorter) because her daughter has started pulling her hair and Lynn is getting sick of putting it in a ponytail. she told Jo, and Jo asked her to wait until after the wedding because she wants all the bridesmaids to have a similar hairdo, dress, shoes, etc. She doesn't want anyone to look out of place in her wedding photos.
My question is, is Jo being unreasonable and/or a bridezilla asking Lynn to not cut her hair? Or is Lynn being unreasonable because it is Jo's wedding, and 4 months isn't that much more time with long hair?