My 18 yr threatening to move out

Good morning everyone....I need some advice... but a little back story 1st: we are a traditional family who believes that there is an age for everything and although controversial, we don't allow our boys to wear girls clothes and vice versa...no we are not opposed to all genders however these are the rules in our home no underage drinking smoking or drug use, no tattoos or body piercings and there is a curfew. 

My 18 yr. daughter has hated the rules since I could remember, she has  cousins 1 yr younger 1 yr older who from a young age were allowed to do these things + wear acrylic nails in elementary school and makeup. I did not. We still do not allow her to drink smoke or engage in drug use(which thank God she doesn't) however she resents the fact that we are against piercings and tattoos. So much so she has threatened to move out next Friday. My husband her father has no idea she has threatened this and my heartbis heavy. Mind you we give her permission to hang out with friends and boyfriend go to movies mall, etc.. don't limit her outfits as long as she is appropriately covered... she says we are old fashioned and does not like this. What do I do? My heart is breaking as all we have ever wanted was to provide a home with age appropriate boundaries and she would rather do what her cousins do. Please any advice would help. If it helps any her older brother had to follow EXACT same rules