What do admission committees look for in a diversity essay?

I'm sitting here with my friend, who is in the process of applying to graduate school. She's come across a prompt that looks like this:

If you are a member of a community that has historically been underrepresented in higher education and would like to tell us how this particular perspective adds to the value you will contribute to the diverse learning community we strive to create, please do so here.

My friend is a female, Latin American, previously financially-burdened immigrant, so there is certainly some diversity to speak of, but she's having trouble coming up with how this can answer the prompt. To her, she's never really considered it a struggle, but more of a challenge. She's never let it get her down, so she sees no reason to complain about it in an essay. She believes you should be judged based on your past and present performance, not your national origin, ethnicity, financial status, etc.

How do you even respond to a prompt like that? Also, why do universities ask you to speak about your diversity in the first place? What are they looking for?