A 51-year-old chronic asthmatic was treated three times for her condition at a Richmond, B.C., hospital before she died, and now doctors say H1N1 worsened her illness.

Mae Mah went to Richmond Hospital on Oct. 31 for a severe asthmatic attack. She had been routinely treated at the facility before. Doctors cared for her and sent her home.

But Mah had another severe attack the next day, and emergency medical workers brought her back to the hospital.

"The second time, she went back by ambulance with shortness of breath and a fever. They told her to breathe through her nose and gave her Tylenol," Mah's daughter, Tiffany Yung, told CTV News.

Mah was again treated and sent home. But after a third visit to the emergency room, her heart stopped. Doctors re-admitted her to the intensive care unit and put her on a ventilator, but she died soon after.

The woman's family say doctors treated her asthma without realizing she had been infected with swine flu, and the virus made underlying health condition much worse.

Experts said detecting swine flu in someone suffering a severe asthma attack can be difficult.

"It doesn't specifically say H1N1," said Winnipeg-based Dr. Anand Kumar. "It does say there is something you want to pay attention to, that there may be more going on than just a routine asthma flare."

Staff at Richmond Hospital are now looking into the incident, as part of standard protocol when a patient dies after repeated care.

"We routinely review cases in which there was a fatality after multiple visits to the hospital to ensure that care was provided appropriately," a spokesperson for Vancouver Coastal Health told CTV News in a statement.

Meanwhile, Mah's family is struggling to come to terms with her sudden death. Mah had been preparing to celebrate Yung's 23rd birthday.

"My birthday's next Monday," said Yung. "She had planned a surprise birthday party for me. I'm devastated she's not here to celebrate."

With a report by CTV's Graham Richardson in Ottawa