A couple of thoughts come to mind Pink.
1. Be totally transparent with your friend. Explain why it was important for you to use the "bet" angle, and tell her how much you valued her support of your changes by helping to keep alcohol away, how touched you are by the party, and ask for your help going forward.
2. Take the "I feel so much better, haven't missed it a bit, I'm going to keep this up" angle. Again thank her for the support, tell her how touched you are by the party, and ask if you can count on her running interference in the future.
3. Tell her you just accepted a 50 year bet. . .
I like the way you labeled this a "slight hiccup" . This team has a plethora of bright folks and together we'll find a solution that meets your needs!