Blazes broke out on Chios in the Aegean Sea on Sunday and tore through 40 square kilometres of mainly bush and pasture land in three days, Greece's climate crisis and civil protection ministry said on Wednesday.
The fire brigade said the woman was arrested on Tuesday night and authorities were still investigating the cause of the fires.
The Georgian was charged with unintentional arson, two fire brigade officials told Reuters on condition anonymity.
Witnesses saw her drop a cigarette, one of the officials said.
Though the wildfires were largely contained by Wednesday, hundreds of firefighters remained on Chios to prevent rekindling and bring all fronts under control, the Greek fire brigade said.
At Europe's southernmost tip, Greece is often hit by wildfires during its hot and dry summers, but authorities say the fast-changing climate is fuelling more destructive blazes.
The Greek government has paid hundreds of millions of euros in damages related to extreme weather to households and farmers and to update firefighting equipment.
It has upped firefighter numbers to a record 18,000 in 2025 in anticipation of a challenging fire season.
They will be assisted by 294 firefighters from five European countries from July 1 to September 15.
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