CarolinaCarol, I don't have any children, but I do believe that your feelings of separation anxiety are natural for a mother who loves her children. It sounds to me like you must have a warm and loving relationship with you daughter and that is extremely special and important. I think that it must be difficult for a parent to let go when a child starts to grow up. Remember how you felt on the first day when your child went to day care or school? I bet you felt a separation anxiety then. I would imagine that a life long of protecting your child makes it difficult to let go, but be happy that she is going to have her first experience in life being that far from home and know that your raised her to be the very best that she can be.
Fear of letting go is a very powerful feeling. And fear is a normal reaction to the unknown. It is this uncertainty and feelings of not having control over the situation or not being there to protect her that probably makes you feel uneasy. Remember that your positive influence in her life is your control factor. I mean that in the best way possible. Your words of wisdom and love will guide her to make the best decisions.
Be proud of yourself for letting her go on this trip. You are giving her freedom which proves that you trust her. That means a lot when you are growing up, or at anytime in a relationship. She will only love you more for giving her this gift of love and trust.
I know I am rambling, but I hope when you start to feel the anxiety upon you, that you will stop for a moment and be proud of you and her and please give her a cell phone before she leaves so that you can stay in touch. 
I hope you and your husband decide to take some time out for yourselves. I think a that sounds like a marvelous idea. Have lots of fun and bring that cell phone with you so that you can call and kiss your daughter before she goes to bed each night.