Can I bring a friend who isn't into any of this?

There is an event I want to go to in a few weeks and I am nervous enough about it that I have been thinking about asking a friend to come with me.

The complication is that she is not into any of this. She knows I am, she is completely relaxed about it, but she would be coming purely as moral support for me rather than because she wants to be there.

Is that alright, or is it a bit off to bring someone who is essentially a spectator? Would she need to dress for it? And if you have done this, did it help or did you spend the whole evening worrying about whether your mate was having an awful time?