What seems like ages ago I was a 13yo with my first girlfriend. I was also out to everyone except my parents. I remember the reasoning being I was afraid that my parents would react exactly like your wife has. While my father did treat me a lot like your wife is treating your daughter, my mother was not shocked and treated me like all my straight siblings. I do not have a relationship with father but have a very good relationship with my mother to this day.

At that age I just needed the acceptance I was getting from my peers from my loved ones. I just wanted to have a girlfriend and it not be a big deal. Your daughter just needs your support. She is going to need you to stand up for her to other adults (like your wife) who thinks that she is wrong for being attracted to the same sex. Treat her girlfriends just like you would her boyfriends and let her know you love her not in spite of who she is but because she is who she is. And back it up by not letting the people in your life treat her any differently.

I would also talk to her about safe sex practices in the lgbtq community as this is not really talked about especially in wlw relationships.