As much as I no longer respect NASA, biggest probability is a medical issue, followed by some problems in her family. Methinks NASA would not make a last minute change for the other selectee...regardless of her credentials.
While speaking of that, could one imagine Dorkbama the Muslim eunuch quota boy even getting through the first hour of astronaut training? (Of course, he could have gotten in. He’d get in with the same quota crap that got him into Columbia and Harvard.)
Has there been physical evidence or credible testimony linking Mr Stubbs* to either of those institutions?
*Obscure literary reference :)