Fink said she didn't go public with the incident at the time because she was trying to build her political career.
The alleged sexual harassment occurred at the fundraiser, where Fink guided Filner from table to table.
One guest told Filner that Fink "had worked her tokus off," Fink said.
"The congressman told me to turn around and patted me on the bum and said, 'Nope, it's still there' and laughed," Fink told CNN.
Fink wrote to Filner's chief of staff and demanded that Filner apologize, she said.
Filner responded, and "he mumbled an apology" and added something "I just did not understand," Fink said.
On Wednesday, Fink told CNN that Filner should resign.
• Morgan Rose
Nonprofit leader Morgan Rose told CNN on Wednesday that she recently told authorities about her experience with Filner after hearing similar accusations against the mayor in recent weeks. She called a hotline set up by the San Diego Sheriff's Department for accusers who are allowed to remain anonymous under California law.
Rose said she met Filner in April 2009 when he was a congressman to lobby on behalf of her nonprofit organization that focuses on domestic violence.
The two met at a restaurant near Filner's congressional office in Chula Vista, California, she told CNN.
At that meeting, she said, Filner allegedly looked her up and down, stared into her eyes and said, "Your eyes have bewitched me," Rose said.
Filner allegedly then made a remark along the lines of, according to Rose's paraphrasing, "You'll have to excuse me for what's about to happen. It's your fault," Rose said.
Filner then moved to her side of the booth, sat beside her, pinned her to the wall, and put his arm around her, Rose alleged.
Rose avoided the advances, and Filner was suddenly interrupted by his ringing cell phone, Rose said. Filner then left the restaurant, she said.
Rose spoke of the incident to her closest friends and didn't pursue the matter because she feared her nonprofit might somehow suffer, she told CNN.
But when Rose heard of similar accusations against Filner in recent weeks, she called the victims hotline.
• Sharon Bernie-Cloward
Sharon Bernie-Cloward, president of the San Diego Port Tenants Association, relayed her allegations against Filner to KPBS, along with three other accusers. She said when Filner was running for mayor in 2012, he approached her at a political event.
"He touched me, actually groped me on my backside inappropriately," Bernie-Cloward told KPBS. "I was left there startled and fearful. In fact, I actually had someone walk me to my car that night."
• Patti Roscoe
Patti Roscoe, a prominent businesswoman in San Diego's tourism and hospitality industry, told KPBS that on numerous occasions, Filner "put in me what I guess now is the famous headlock."
"I felt fearful, even as well as I knew him, because it was an invasion into my space," Roscoe told the network. "And he would come in and try to kiss me on the lips and I'd have to squirm to get away. And just as recently as a few months ago this happened. I turned and he just slobbered down my chin.
"And I was so violated and so offended. It's just such a terrible invasion."
• Veronica "Ronne" Froman