To find out how much sugar she used, multiply the total amount of sugar in the canister by the fraction she used.
She has \( \frac{7}{8} \) cups of sugar and uses \( \frac{1}{2} \) of it:
\[ \text{Sugar used} = \frac{1}{2} \times \frac{7}{8} \]
To multiply these fractions, multiply the numerators and the denominators:
\[ \frac{1 \times 7}{2 \times 8} = \frac{7}{16} \]
So, she used \( \frac{7}{16} \) cups of sugar for the dessert.