Answer:
If she wants at least one comedy, there are 1484 different combinations.
Explanation:
The order in which she wants to pick the movies is not important. So, we use the combinations formula to solve this question.
Combinations formula:
is the number of different combinations of x objects from a set of n elements, given by the following formula.

In this question:
She wants combinations of 3 movies, with at least one comedy. The easiest way to find this is finding the total number of combinations of 3 movies, from the set of 25(18 children's and 7 comedies), and subtract by the total number without comedies(which is 3 from a set of 25). So
Total:
3 from a set of 25.

Without comedies:
3 from a set of 18.

At least one comedy:

If she wants at least one comedy, there are 1484 different combinations.