Complex sentence: During this time Curtiss was the only person who had worked with her to have any regular contact, meeting once a week to continue testing, and wrote that Genie's speech severely deteriorated due to the abuse she endured.
Split into simpler sentences: During this time, Curtiss was the only person who had worked with Genie to have any regular contact with her. They met once a week to continue testing, and Curtiss wrote that Genie's speech severely deteriorated due to the abuse she endured.