A Trowbridge woman suffered minor injuries in a suspected arson at flats in Charlotte Square on Friday evening.
A mattress was set on fire in an incident at the ground floor flat, where the injured woman is believed to live, at 11.17pm. Fire crews used six hose reels to tackle the blaze.
A ambulance was called, with paramedics tending to the woman, who had minor injuries.
The 22-year-old woman, who has a history of mental health problems, was taken to the Royal United Hospital Bath, for further checks as a precaution.
She was arrested on Saturday on suspicion of committing arson with intent to endanger life.
No-one else was in the flat at the time, but 10 other tenants were temporarily evacuated from the building.
Police are still investigating and any witnesses are asked to contact the 101 number.