Hey again Little Coojy.
I honestly think that the best thing to do is stand by what you know is best for your daughter.
One option that is less 'on the leash' and will allow her more responsibility would be to ask her what time she feels would be appropriate to be back at.
Its what my Dad did for me, and it gave me the chance to express my feelings, and also to talk options over with him, without feeling controlled.
We agreed that unless it was a specific occasion - such as a party, that i would be home by 8:30 and in bed by 11:00. Because i had helped to set my own rules, it made them easier to stick to as well.
I know how hard it was for my Dad to let go, and never having had children myself, i can't imagine what it must be like to watch them grow up and gain maturity. I guess it would be like my kitten leaving home, but intensified by like a million - which sounds unbearable!!!!!!!
(hope it helps to have the perspective from someone who was in your daughters position 2 years ago, as well as opinions of fellow parents.)
stay strong, your daughter won't stop loving you. xx