How to congratulate my crush for her prom?

For now I am friends with this girl, and today is her prom. I am few years older than her tho, and I want to text her congratulating her, but I was wondering if should include a heart emoji in my text. We are kind of close-ish friends, tho we met recently about two months ago. I feel like she doesnt expect I have a crush her. Is the heart emoji too obvious?