My sister is 12 years of age and got 96 on her iq score. i know that anything under 100 is below average. should i be worrying?

No: Half of humankind is "below average" by definition on any measure. Not everybody is meant to be a star student, and the standard iq tests are really measures that predict academic success. The happiest guy in the town in which i grew up was a tramp who did day work. And i became much happier when i stopped worrying about others' gifts ; resolved to use my own modest talents to be helpful to others.

Meaning of IQ Scores: In school, we get used to being graded out of 100. But intelligence tests work on the principle of averages. Consider the average height for a woman in the US (5' 4"): It turns out that 68% of women are between 5' 1.5" - 5' 6.5" tall. On the Wechsler Intelligence Scale (commonly used), the average Full Sc score is 100. BUT 68% of people obtain a Full Sc core in Average range, between 90 & 109.