Rivers State health commissioner Sampson Parker said test results showed the woman had the disease, which claimed the life of her husband, Ike Enemuo, on August 22.
Enemuo fell ill and died after treating an official from the ECOWAS regional bloc who travelled to Port Harcourt after having contact with a Liberian man who brought the virus into Nigeria.
The doctor was the sixth to die from the virus in Nigeria and the first outside Lagos, raising fears about the spread of the haemmorhagic fever just as it was thought to have been contained.
Sampson said three patients — another doctor, a pharmacist and a woman who had contact with Enemuo at the hospital where he died — had been taken to a specialist treatment centre outside the city.
Enemuo’s widow was at an isolation unit in Lagos, he added.
“They have not been confirmed (as having Ebola) and we are waiting for the result of the investigation,” he told a news conference.
Some 200 primary and secondary contacts have been traced, although about 60 had yet to be spoken to, he added. None of them had shown symptoms, he said.
“We are concentrating on the names we have to capture in our (monitoring) activities but the good news is that we have been making good progress in checking the spread of Ebola,” he said.
Parker said early detection and treatment was vital, appealing for anyone who had contact with Enemuo, his clinic, the ECOWAS official or the hotel where he stayed to contact them immediately.
Of the 15 confirmed cases in Ebola, seven of the patients recovered, the government in Abuja has said.
The ECOWAS official is also thought to have recovered.
Nigeria is one of five countries in West Africa hit by Ebola, although the majority of the more than 1,500 deaths since the start of the year have been in Liberia, Sierra Leone and Guinea.