Step 1: Understanding the Question.
We need to pick the one film among four that was NOT made by Mira Nair, so the fastest route is to sort the titles by their actual director rather than by trying to recall Mira Nair's full list first.
Step 2: Key Approach.
Group the films by director. Three of these titles share one director; the fourth belongs to someone else. Spotting the odd filmmaker out solves the question directly.
Step 3: Detailed Explanation.
Salaam Bombay (1988) launched Mira Nair's career and got an Oscar nomination for Best Foreign Language Film.
Kamasutra: A Tale of Love (1996) is also her work, a period romance set in 16th century India.
Monsoon Wedding (2001) is her best-known film internationally, following a big fat Punjabi wedding, and it won the Golden Lion at Venice.
Earth (1998), on the other hand, is directed by Deepa Mehta, and it forms the middle chapter of her Fire-Earth-Water Elements Trilogy. Mira Nair had no involvement in Earth.
Step 4: Final Answer.
Since three films trace back to Mira Nair and Earth traces back to Deepa Mehta, Earth is the film not directed by Mira Nair.