I'd say the sentence still makes sense without the boldened part. Does it contain any meaning and if it does, why is it there? what extra meaning does it contain?A smug and smiling Stronach didn't just betray Conservative Leader Stephen Harper and humiliate Deputy Leader Peter MacKay, both politically and personally. She also betrayed her constituents in the riding of Newmarket-Aurora.
In the UK, 'riding' was a subdivision of a big county (region). It sounds here as if it has a simialr meaning, but I'm not Canadian. Maybe Cas will be able to inform us.