The woman and her four children were woken up during the night by a fire inside their apartment in Haninge, Stockholm County, which had started to fill with smoke. Police suspect someone poured flammable liquid through her letter box then set fire to it.
The woman managed to extinguish the flames, but was taken to hospital in shock after the alarm was raised at around 02:30.
"This was no accident," Stockholm police spokesperson Ulla-Britt Öhman said.
The apartment is now cordoned off while a forensic investigation is carried out. There are currently no suspects, but police are treating the incident as arson.