In his own home? Castle doctrine. In fact, he'd be entirely within his rights under Texas law to attack and kill her - "The actor's belief that the deadly force was immediately necessary as described by that subdivision is presumed to be reasonable if the actor knew or had reason to believe that the person against whom the deadly force was used unlawfully and with force entered, or was attempting to enter unlawfully and with force, the actor's occupied habitation, vehicle, or place of business or employment."