Really, what was her reasoning?
She's a Democrat-turned-Independent who has been getting more Conservative in recent years (especially on social issues).
She supported Jesse Jackson in 1988, Bill Clinton in '92 and '96. But then both she and my dad were turned off by Bill Clinton and voted for Bush out of contempt of Clinton. My dad became your typical Republican while my mom became an Independent. She ended up not liking Bush any more than Clinton and voted for Nader simply out of a rejection of the two-party system. After Nader she voted for McCain and then in 2012 reluctantly voted for Romney. I remember at the time people made fun of her for voting for Nader (and it still gets brought up among our friends who are more loyal Republicans).