Complex sentence: After two months, in mid-October 1971, Curtiss saw that Genie was clearly listening and responding, and had begun paying attention to people even when they were not speaking directly to or about her.
Split into simpler sentences: After two months, in mid-October 1971, Curtiss saw that Genie was clearly listening and responding. After that point, she wrote that Genie began to pay attention to people even when they were not speaking directly to or about her.