Around seven months after losing the race for mayor of Los Angeles, Greuel said she will be putting all her effort into the new campaign.
"I'm excited. If you can't tell I'm passionate about this. I'm ready to be that champion," Greuel told Eyewitness News on Thursday.
She had no idea she would be a candidate, but after hearing that Waxman planned to retire at the end of this term, she said she instantly knew.
"It's a quick decision. I knew it was right. I knew in my gut this was an opportunity for me to serve this community," she said.
Greuel is not alone in her ambitions. Sen. Lieu announced his candidacy on Friday. In a statement, Lieu cited his various accomplishments as senator and said he would fight hard for his constituents in Congress as he has done in the state Senate.
The statement listed 25 elected officials as having already endorsed Lieu, who has also served on the Torrance City Council and the California Assembly in addition to the state Senate.
In addition to Greuel and Lieu, liberal activist and attorney Sandra Fluke says she's strongly considering running for the seat. Fluke is the former Georgetown University law student who testified to congressional Democrats that she wanted her college health plan to cover her birth control. Radio personality Rush Limbaugh branded her a "slut," but later apologized.
Democrat state Sen. Fran Pavley is a possible candidate, as is independent Bob Bloomfield, who nearly defeated Waxman two years ago.
Waxman announced his retirement plans on Thursday. The 74-year-old is one of the last of the post-Watergate class and represented the 33rd Congressional District, covering Palos Verdes, Beverly Hills, Santa Monica and Malibu.
President Barack Obama described Waxman as "one of the most accomplished legislators of his or any era."
His signature legislation includes nutrition labels on food and stronger warning labels on tobacco products. He was instrumental in passing the Affordable Care Act.
Waxman was also a champion of environmental causes. He was one of the chief architects behind a 1990 upgrade to air pollution laws, and in 2009, along with then-Rep. Ed Markey, D-Mass., co-wrote the only bill to control global warming to have passed the House. The legislation, backed by the Obama administration, died in the Senate.
Waxman will retire in January after 40 years in Congress.
The Associated Press contributed to this report.