If you don't think you'd enjoy it don't go, don't do what all the other people are doing, i.e. say they'll go then text at the last minute saying they can't cos that is a bit bitchy. One of my rules is always if i don't enjoy something i don't do it, cos i always know while i'm doing it that i could be doing something better. Don't do something cos its convenient for someone else. Think up a good reason for not going and tell her, you don't have to lie you could plan something and just bend the truth a little and say you have a previous engagement (which you'll make as soon as possible). But if you know you won't enjoy it ther is no earthly point in doing it and no good reason why you should.