I always attributed Guinan's ability to her species too, but there's also the following...
It was unclear if Guinan's special abilities and perceptions in regard to time and her ability to perceive Q were completely the result of her lineage, or if they were an extra side effect of her experience with the Nexus. According to the novel The Buried Age, Guinan's abilities were due to the echo of her left within the Nexus. This concept originated in an unfilmed scene in the Generations screenplay.
Not canon, but it was interesting enough to go by.