Barbara Ruth Brand also admitted that she used a gun to kill 57-year-old Paul Slysh. She faces up to 10 years in state prison when she is sentenced Feb. 15.
Deputy District Attorney Amy Maund said Brand shot Slysh in the back, side and front torso area on the afternoon of July 12.
Slysh was taken to a hospital and was originally expected to survive, but he died two days later.
Maund said Slysh and Brand had been off-and-on roommates for several years.
Police said Brand made an emergency call shortly after 4:30 p.m. to report that she had just shot Slysh in their home in the 1500 block of Morena Boulevard.
Brand told arriving patrol officers she had opened fire on the victim because she was angry at him, SDPD Officer David Stafford said.