What's done is done. They are going to get married whether you like it or not, she is an adult and can do as she pleases. Perhaps she was scared of you reaction (and rightfully so) as you seem not happy for her and want to embarrass her by trowing a fit and sabotaging the day by not attending.
You role is to be supportive of your children. She is happy and getting married and you need to get over yourself and put your ego aside. You did what you could to raise her and she is an adult now. You cannot control her actions anymore. You cannot force them into counseling or expect them to postpone their nuptials just because you said so. You do not live with her, nor have any right to impose orders on your adult, grown daughter.
My advice is to wish her best and support her. Attend with a smile on your face and be helpful, charming and selfless. It is not fair to her to reflect your own issues on her and to tag her with YOUR baggage, she is a different human being than you.
Sure, counseling seems to be a great idea, but there is no time for that, leave alone 6 months worth. Most couples go to just one session, maybe two. They have made up their minds and they are getting married. Making it about you and your issues and sabotaging her day is not going to make her happier or more successful. If you want to be part of your daughter's life, I suggest you attend and leave your comments to yourself.