The first thing I would say to you is feel your sadness and allow yourself to cry. Of course this is a huge shock to you, news you need to get your head and your heart around.
I don’t know how any parent can say they have no difficulty in your situation as the majority of us are brought up in Ireland as part of the conservative, heterosexual society. It takes some getting used to when one of your offspring tells you this.
I think you need to talk to someone confidentially that you trust. You need someone to talk to for you right now and I do not think it is fair of your daughter to silence you. Talk to a sister or a good friend and let them know how you feel.
There are some good support systems available from the HSE for your daughter and family members in this situation. They will also direct you to other organisations who can offer help and support.
You do know that you will always love your daughter, no matter what. I know from your letter that you love her unconditionally and your love for her will conquer all!
Regardless of her sexual preferences, she will always be your chlld and you will be there for her and she knows this as she trusts you enough to be the first to tell. Give yourself credit for this fact, and get yourself some support because, as you say yourself, you do not want to say the wrong thing to her at such a tender age in such a sensitive time.
From reading your letter, I think you will cope very well once you get your own help and support.