Geared towards the ladies here. I need help figuring out how to avoid a landmine?

My cousin is taking her GMAT on Sunday and she is freaking out. So, I told her that I would take her to an opera on Saturday night in order to relax her. I also invited a friend of mine to the opera, since she is a musician and appreciates the arts. She is an awesome friend. What I am afraid of is that she might have misinterpreted the outing as a date. I honestly hadn't considered it until someone had told me to make it clear to her in order to avoid confusion. In hindsight, inviting someone to an opera on a Saturday night is prime date material. How do I enforce the idea that the outing is just friends hanging out and not a date? She's awesome and I want to avoid messing up the friendship.