whats with girls bringing other girls down?

I was in a friend group with 3 other girls, we were hanging out and one of their brothers who was with us cause we wanted to be out late and her mum wanted to know she could atleast have mlre then one person to contact, was with us
he saw a girl and said she's pretty and asked if he should go over and ask for her number

now one of the girls likes him and she starts saying some nasty stuff about the girl, commenting on her hair, makeup, and over all appearance!
i havent spoken to any of them since because what the hell? women, can we PLEASE start standing up for eachother instead of bringing eachother down? ESPECIALLY when theres a man involved!

anyway have a good day/night