Never underestimate the power of having a strong connection with your significant other. Clearly, she has more attractive options. Clearly, she is making a huge sacrifice (literally).
Women don't draw up a list of pro's and con's about guys--it's not a rational process. This is where all the Darwin stuff goes out the window--if it was really "survival of the fittest," you would not see ANY able-bodied women with disabled men. He probably has a fun personality, a positive attitude, and the ability to connect with her and command respect from her. Most importantly, he probably doesn't run his love life based on the principle that woman will go for the highest value male they can find, and if a better deal happens to come to her, he's screwed. That kind of thinking is the antithesis of the "prize" mentality.
The evolutionary biology stuff on sosuave is based on extremely broad generalizations of a very unique and intricate species. Take it as a very interesting theory or a general guideline of understanding female behavior, but don't let it lead to paranoia in your dealings with women.
I DID find it funny that her previous husband was overweight, too. . .what a chubby chaser.