"The high death rate, the overwhelming numbers of patients, the lack of effective treatment, and obviously the personal risks of being infected yourself, made it extremely challenging," she said.
"I had about one day off the whole time. It was busy and very challenging, but overall very satisfying and energising too."
Before leaving to help deal with the biggest outbreak of the disease in history, Dr Mills said: "This is a major public health crisis and Sierra Leone is a very poor country with few resources to deal with it.
"They need support from us."
Her message is the same on her return.
"It's a country that's come out of a decade of civil conflict. It's got a life expectancy of about 50. A lot of the population lives on less than $1 a day and certainly [the Ebola outbreak] has had a huge impact on the health system."
Despite the country having a better handle on Ebola now, the repercussions will be long-lasting, Dr Mills said.
The number of cases started dropping late last year and by the end of February some make-shift clinics were closing.
Dr Mills said the reduction was due to a combination of reasons, including treatment being available, contact-tracing, community engagement, travel bans, quarantine and controlled burial practices.
Fatality rates were up to 70 per cent at the viral disease's peak in western Africa last year. Symptoms are fever, vomiting and diarrhoea and bleeding. It is spread through contact with infected body fluids.
Since March 2014, the virus has infected more than 25,000 people, with more than 10,000 deaths reported.
