Ways to get my sister to her surprise party?

Okay, my sister is turning 17 and we've been planning a huge party for her at a nearby park by our house. We got everything settled except how to lure her to the park. I was thinking to tell her, there were hot boys playing basketball and to fix yourself up, but really her party is happening. I need a more believable idea. And I need some entertainment like games for her party, it will be a mixture if guys and girls, there's already a dunk tank, water balloons, and an inflatable boxing ring. Any game ideas?? Kthanks (: