The blaze was reported shortly before 5am at a home on Monastery Grove in Enniskerry, Co Wicklow.
Gardai said two children aged 15 and 13 fled from the house and suffered only minor injuries.
The woman was found dead in an upstairs room of the home.
Gardai are carrying out a technical examination of the scene but the fire is not being treated as suspicious.
The two children were treated at Crumlin children's hospital.
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