Answer:
Sally is wrong because in fractions, the greater the denominator, the smaller the fraction.
Not to mention if you look at it like 1/4 vs. 1/3, 1/3 is bigger because it is a third, while 1/4 is a quarter. So 3 quarters (3/4) is not even close to being bigger than 2 thirds (2/3).
Hope this explanation helps :)