A 13-year-old Mansfield girl died Wednesday at school after an apparent asthma attack.
Tiffany Phu, an 8th-grader at Brooks Wester Middle School, died after she had just run two miles, her family said.
"It happened out of the blue,” said her sister Michelle Phu. "The last thing my mom saw was her smiling at her when she was running on the track and she collapsed."
Phu's two older sisters and younger brother wanted to talk about her and the issue of asthma.
According to the American Lung Association, the chronic lung disorder affects more than 7 million children.
"I feel sad and angry,” said 11-year-old Nicholas Phu.
Phu’s older sister Faustine Phu, a recent graduate of medical school, said Tiffany knew she had asthma and frequently used an inhaler to help her breathe, but appeared to be in good health.
"When I heard the news it just hit me really hard,” Faustine Phu said. “"She wasn't sick at all. It makes me scared about the methods we use to control asthma, if it's even enough."
Michelle Phu, 18, said people need to understand how serious and unpredictable an asthma attack can be.
Tiffany Phu was athletic and loved to play soccer and run, she said.
"It was sudden,” Michelle Phu said. “I know her. If she had trouble breathing, she would have sat down and, you know, asked for water or something."
At school, her friends are remembering her with a makeshift memorial in the front hallway.
A vigil is set at Wester Middle School for 8 p.m. Friday.
NBC 5's Scott Gordon contributed to this report.