Based on the information in the news account, one can speculate that prominent "underlying condition" was unfamiliarity with a drastically different climate from that of Ohio, her home.

She was almost certainly not well hydrated, being unfamiliar with the demands of Arizona climate. They were planning a multiday trip, so probably plenty of weight. Did they start early enough? 4AM would not be too soon. The last time I hiked at Grand Canyon in the summer, I started at 230 AM.....

The park brochure of back country hiking gives solid, time tested guidance, but this group would not have been the first to disregard....