The Washington Post reported in February Napolitano was making it known she was considering a run.
The former Arizona governor told reporters Tuesday, "That kind of contemplating would keep me up at night, and I lose enough sleep at night as it is."
She added she was optimistic about talks on immigration reform being held by eight senators from both parties, the Washington newspaper The Hill said.
"I think now is the time. I think the election had consequences in that regard," referring to President Barack Obama winning more than 70 percent of the Hispanic vote in the 2012 election.