This is apparently because she didn't want her co-star, Hrithik Roshan to waste his dates. Even though she was sick, she reported on the sets in time, much to the surprise of the unit members and didn't throw any tantrums.
According to a source, she continued shooting, in spite of having fever for two days, as she wanted to make it convenient for Hrithik, it being the last two days of his first schedule.