"Hardly fair" You decided to changes the rules right at the last minute and didn't tell us about it.
If you had said that your sister would be picking a random number from the start then results would have probably been different.
So no you didn't make it fair you made it unfair, but in all honesty i don't believe that to be the truth anyway, i believe you went with your original idea and picked the person you believed deserved the game the most and without wanting to flip everyone else off came up with the idea that your sister chose the winner without her knowledge.
Anyway congrats Meatloaf, enjoy!

Nice of the OP to do this in the first place! Pretty rude reaction if legit