A 25-year-old woman has been charged after allegedly firebombing a home in Theodore and assaulting another woman during a family violence incident on Tuesday night.

Police allege the woman sent threatening messages to her partner and members of his family between Sunday and Tuesday, threatening to injure them and damage homes and businesses associated with the family.

About 9.10pm on Tuesday, she allegedly threw a homemade incendiary device at a Theodore home, causing minor fire damage.

The woman also allegedly assaulted another woman known to her at the property.

Police arrested the 25-year-old at the scene and allegedly found a pocket knife, lighter and another incendiary device nearby.

Officers later searched her vehicle and allegedly found two more improvised incendiary devices.

She has been charged with arson with intent to endanger life, common assault, possessing a knife without reasonable excuse and using a carriage service to menace.

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