They are two separate essays.

The one for swimming is:Tell us about the most significant challenge you've faced or something important that didn't go according to plan. How did you manage the situation? (250 words max.)

The one about the piano is: Tell us about something you do for the pleasure of it. (100 words max.)

"She explained that success is not natural, and that she had had to work incredibly hard during college to become fast." You need a present verb tense first, and then a past pluperfect verb tense.

Both are fine.