Annamaria Magno Gana, 41, was taken into custody shortly after the 4:30 p.m. shooting at a home on the 18400 block of Manning Avenue, Orange County Sheriff's spokesman Jim Amormino said.
When deputies entered the home, they a 9-year-old holding a high-powered rifle and two people hit by gunfire. Both were transported to a local hospital.
Gana's husband, Antonio Potenciano Gana, 72, was later declared dead. Her 16-year-old son was listed in critical condition.
The young boy had allegedly wrestled the gun from his mother, reports said.