To rewrite the expression \(\frac{1}{1 - \sin \theta}\) so that the denominator contains \(\cos^2 \theta\), we can use the identity:
\[ 1 - \sin^2 \theta = \cos^2 \theta \]
This means we can express \(1 - \sin \theta\) in a form that involves \(\cos^2 \theta\) by multiplying the numerator and denominator by \(1 + \sin \theta\).
Doing this gives:
\[ \frac{1}{1 - \sin \theta} \cdot \frac{1 + \sin \theta}{1 + \sin \theta} = \frac{1 + \sin \theta}{(1 - \sin \theta)(1 + \sin \theta)} = \frac{1 + \sin \theta}{1 - \sin^2 \theta} = \frac{1 + \sin \theta}{\cos^2 \theta} \]
Thus, the correct response is:
She can multiply the numerator and denominator by \(1 + \sin \theta\).