Cordero and the rest of his family were with Josie during her final moments.
The right-hander, who has been on the bereavement list since Tuesday, went back to Southern California to be with his grandmother, who had brain cancer. He said she also had a broken hip from an accident she suffered a few weeks ago.
Cordero said that his grandmother's illness was affecting him on the mound. On Sunday, he had a tough time throwing strikes and gave up the game-tying run in the ninth inning against the Cubs.
"Having her on my mind the whole time was hard," Cordero said by phone on Friday. "You knew how much she was suffering, and not being able to be there was kind of hard."
Cordero informed manager Manny Acta on Monday that he had his grandmother on his mind, and both originally agreed that Cordero needed at least two days off.
Josie Cordero was like a second mother to the right-hander. Cordero said Josie always went to his baseball games while he was growing up in Southern California.
"Spending time with my family has been good," the closer said. "I had my family on my mind a lot the last couple of weeks. I will now come back and focus on baseball."
Cordero said he expects to travel back to Washington on Sunday night and rejoin the team the following day.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.