As they say "Living Well is the Sweetest Revenge".

Dress like a rock-star, arrive at the event smiling, happy, and blissfully unconcerned about her little lie. If she brings it up, be forgiving and dismissive, as if you hadn't noticed. Afterall, you were just doing her a favour in the first place, right? So she wouldn't be an unaccompanied female?

Have a great time.