Born in Fredericton, New Brunswick, Henry grew up in Charlottetown, Prince Edward Island, where her mother, father, sister, niece, and nephew live.

[4] Her father was a major in the Canadian Army; the family lived in many different locations due to his postings, including Calgary, St. John's, and the Netherlands.

[2][7] In the early 2000s, Henry served as part of the World Health Organization (WHO) UNICEF polio eradication programme in Pakistan.

In this capacity she was operational lead of the response to the severe acute respiratory syndrome (SARS) and Influenza A virus subtype H1N1 outbreaks in Toronto.

[5][14] She helped to lead British Columbia through a catastrophic wildfire season, which impacted the air quality, as well as advising the Government of Canada on the Influenza A virus subtype H7N9 epidemic.

[15] In 2015, she testified as an expert witness alongside Allison McGeer in a labour arbitration between the Ontario Nurses' Association and Sault Area Hospital regarding a "vaccine or mask" policy.

[17] Henry has taught at the University of British Columbia School of Population and Public Health, and the Faculty of Medicine since 2010, where she is an associate professor.

[31] In June, Henry was featured in a New York Times article titled "The Top Doctor Who Aced the Coronavirus Test", praising the way that she has handled the COVID-19 pandemic.

[21] In August, September, and October 2020, Henry was criticized for not mandating public mask usage and BC's back to school plans.

[33] A limited edition Compass card featuring the quote from Henry, "Be Kind, Be Calm, Be Safe" was released by TransLink on September 15, 2020.

"[35] In November 2020 the Public Health Agency of Canada (PHAC) stated that BC was no longer saying what proportion of people who tested positive are healthcare providers.

[27] In 2022, internal emails obtained by members of the press showed that Henry and other BC public health officials had been aware of concerns about BC's COVID-19 school transmission data, including a "daunting" spike in exposures, while having publicly claimed that transmission was very low and parents shouldn't worry "needlessly".

[40] Earlier that year, Henry had co-authored a peer-reviewed study documenting a steep increase in COVID-19 infection in Metro Vancouver and the Fraser Valley in 2022, with the highest numbers among children and youth.