I doubt that she went from being totally fine to suicidal because of the prank. But I can absolutely see the prank, and its professional consequences, being the last straw for someone who's already depressed. The DJs should be held responsible because they knowingly picked a mark who could very easily be identified.
I try to keep in mind that anyone I interact with may have depression or similar issues. After all, so many people do.
You never know what battle another person is fighting or what demons they have going-on in their head. It's so sad.