Every few years, somebody on "Wheel of Fortune" mispronounces a word solving a puzzle they obviously know and loses out on a bunch of money. Every few years when that happens, "Wheel of Fortune missolve" starts trending and there's a collective outrage of "WTF they should have won", even though that rule has been consistently enforced for over 40 years and there's tons of precedent to back that up. It's fair, but that doesn't stop it from making the news in a negative way over and over.
If fairness is the number one issue, she absolutely should have been ruled incorrect and sent off with a "well, we're guaranteeing your charity $32,000 despite the mistake." It isn't fair to the other contestants who made that same mistake and were ruled incorrect if you break that precedent.
But fairness isn't the number one issue. The goal of Millionaire is to make good TV. If I'm Michael Davies, I don't want some controversial decision like that happening on the second episode of my big primetime event, getting the show trending for the wrong reasons, and overshadowing the rest of the series.
I don't like the decision and I think she should have been ruled incorrect, but I see why it was made. Chalk it up as "famous people don't get held to the same standard as regular folks", volume #16,000.