The woman was not a Suksapan Panit employee, its manager Pavit Pangwiwat said.
The shop is located at the two-storey Planetarium on Sukhumvit Road in Klong Toei and was closed at the time because of the national holiday.
Pavit returned to work on Wednesday to check the shop’s electronic system and was informed about the fire by the shop’s security guard
Supuktrapon Wongsuwan, 36, was then found choking on smoke inside the shop and rescued.
Supuktrapon confessed to multiple other thefts, including stealing donation boxes at Wat Suan, Vejthani Hospital and The Mall department store. She said she needed the money to care of her children.
The fire was started on the second floor and was extinguished in about 10 minutes by eight firefighters.
The chief of Metropolitan Police Division 5, Maj-General Somprasong Yentuam, told a press conference that Supuktrapon hid in the shop’s storage room on the first floor.
When the shop closed she stole money from the donation box but could not get out so she started the fire by burning a mouse pad with a lighter, he said.
Police said she committed similar crimes on November 23 after being released from prison for burglary about seven months ago.