The woman was pulled out of the house, where the fire was thought to have started between 3.30am and 6am on Sunday.
It began in a bedroom, where it was confined by firefighters, but other parts of the house had fire and smoke damage.
The woman's death comes soon after that of Hastings 10-year-old Ariki River Baden Mau, who was rushed to hospital last Monday afternoon after being involved in a suspicious fire in a derelict building on Heretaunga St West.
He died the next morning.
A 9-year-old boy also taken to hospital in a serious condition was last night in a stable condition in Hawke's Bay Hospital after receiving treatment in Hutt Hospital.
Fire services were called to another suspicious blaze in Onekawa at 6.30pm on Friday which continues to be investigated.
Emergency services were called to the house fire on Roberts Tce, Onekawa, where a car and garage attached to the address were fully involved in flames.
The occupants had safely evacuated and while firefighters were able to contain the blaze, the car and garage were "completely destroyed" and the house suffered some fire damage.
Charred remains are all that's left of another residential property on Marine Pde that was gutted by an "unexplained" fire in the early hours of Sunday.
Firefighters were called to the Napier house at 5am where the fire was "well involved" with the structure, and put it out by 7am.
No one was home at the time of the fire and on Sunday police asked anyone who saw suspicious activity in the area to contact them as soon as possible.
Hawke's Bay Fire area manager Ken Cooper said having two deaths in the past week was an "outlier" in regards to the annual toll of fire deaths in Hawke's Bay.
He said there had been seven fatalities in Hawke's Bay since 2011 - zero in 2011, three in 2012, one in 2013, one in 2014, zero in both 2015 and 2016 and now two in 2017.
He said firefighters were hugely affected by fire fatalities, and were trying to reinforce the importance of having working smoke alarms and an escape plan, and educating young children about the dangers of fire.
"It certainly does have a huge impact on us as firefighters and we definitely reflect on what we're doing and how we're responding to the community," Mr Cooper said.
"We do a lot of self analysis and self reflection on fire fatalities and always look to see how we can perform better."