The room was kept as it had always been: on a writing desk in front of the window, a lamp and a pile of award certificates, proof of Zhang's striving for excellence as a student, was collecting dust. A teenage Zhang once sat there studying into the wee hours. Once in a while she might have looked up and peered into the world map covering an entire wall on her right side.

It's a world she had set out to explore, as she journey from her native town to the bustling coastal city of Guangzhou 850 kilometers away to attend one of China's top universities, where she met Hou, her classmate. After they graduated in 2016 both were enrolled by the prestigious Peking University, Zhang in its master's program and Hou in its doctoral program. By the time Zhang left for the US, she had completed her studies at Peking University, before working briefly at the Chinese Academy of Sciences.

"Growing up, I didn't have a lot of opportunities playing with my sister－she was always up there studying," said Zhang Xinyang, Zhang Yingying's younger brother."But she never failed to turn up wherever I was beaten up or bullied by older kids.

"I'll support him as long as he agrees to work hard," wrote Zhang in her diary, faulting herself for not having cared enough for her younger brother, who quit school when he was 15.

She also harbored guilt regarding her parents.