COLUMBIA - Saying that her role as the agency's chief was "causing a distraction," the state's embattled Department of Social Services director resigned Monday.

Lillian Koller's resignation letter was made available by the Governor's Office. Koller worked at the agency for just over three years, after being appointed in 2011. Amber Gillum, deputy state director for DSS' Economic Services, will serve as the agency's interim director until a permanent replacement is appointed.

DSS has been the subject of an ongoing investigation by a Senate oversight committee after a few child welfare officials voiced concern over several deaths of children who had case files with the agency. The panel has been asked to report to the General Assembly on how to improve the agency. As the investigation unfolded, several lawmakers called for Koller to resign or for Gov. Nikki Haley to fire her.

"It has become more and more apparent to me during the past few weeks that my being the State Director is causing a distraction and making it more difficult for DSS to continue the measurable improvements made to the agency during my tenure that have improved the lives of the citizens we serve," Koller wrote in her resignation letter. "It has been a privilege and pleasure to work with you, Governor."

Gov. Haley said in a written statement that Koller put the well-being of South Carolina's children above her own. Haley added she will continue to be proud of Koller and the work she's done at DSS.

"Lillian Koller is a dedicated public servant and child advocate, and a wonderful and loving mother - and I am so grateful for her service to South Carolina," Haley said. "Under her leadership, DSS closed a $28 million deficit, moved more than 20,000 South Carolinians from welfare-to-work, and has done wonders to improve our foster care system, placing more South Carolina children in stable, healthy families."

In recent weeks, the chorus of lawmakers frustrated with Koller had grown. Sen. Marlon Kimpson, D-Charleston, and Senate President Pro Tempore John Courson, R-Columbia, joined Sens. Katrina Shealy, R-Lexington, and Joel Lourie, D-Columbia, in calling for Koller's resignation.

When reached on Monday, Kimpson said he had mixed feelings about Koller's resignation. Kimpson was the only Lowcountry lawmaker who called on Koller to resign.

"This is a first step in reforming a system that has failed our children," Kimpson said. "We now need to look at Mrs. Koller's executive, regional and local leadership teams to make sure that the incompetence has not spread downstream, so that the problems that have plagued DSS since she was appointed are not still there."

Charleston County Coroner Rae Wooten, who called for reform at the agency in March, said problems at DSS were bigger than one person.

"We can remove any one individual, but we still need to address the problems within the agency," Wooten said. "She's (Koller) been at the helm, but the bottom line is that the same issues will be there afterward unless there is an effort to get down to the root of the problem and make changes."

Shealy also acknowledged that problems at DSS predated Koller, but said that they haven't improved since Koller was appointed. Shealy is one of three members of the Senate DSS Oversight Committee investigating the agency.

"I think it's the best thing for South Carolina," said Shealy, adding that now panel can move forward. "We need to work together to solve this problem because this is about children. This is not about any individual; this about South Carolina and her children."

Shealy and Kimpson were two of seven sponsors who introduced a resolution in the Senate on Thursday that would have declared the legislative body had no confidence in Koller's leadership. The resolution received bipartisan support, with four Republicans and three Democrats as sponsors.

Lourie echoed Shealy's sentiments as far as lawmakers and DSS staffers working together to fix the agency's issues. He added that the oversight committee and the House will now work together as well to restructure DSS.

"Today is not a day, in any way, to celebrate," Lourie said. "Certainly removing Lillian Koller from the equation is not going to fix all of the problems at DSS. That's just a starting point."

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Democratic gubernatorial candidate Sen. Vincent Sheheen, of Camden, called Koller's resignation a needed step in protecting South Carolina children.

"I don't want it to detract from the fact that there are serious problems at the Department of Social Services that go beyond just one person," he added.

The Senate panel, which is scheduled to meet on Wednesday, will now have to readjust its schedule. Koller's presence had been requested, but she is no longer expected to testify. Sen. Tom Young, R-Aiken, said he had asked Koller to testify about data the panel received late last week, concerning child welfare caseload.

On Wednesday, The Post and Courier published a story that revealed nearly a third of DSS workers were shouldering larger than recommended caseloads for the month of May, according to internal preliminary reports. The numbers differed from a reported statewide caseload average of six per worker, a number frequently repeated by agency leaders.

Unlike Shealy and Lourie, Young never called for Koller's resignation or firing.

"I felt like it was important, as the chairman of this subcommittee, that we keep our subcommittee focused on the big picture, which is what we are charged to do and keep us moving in that direction," Young said. "I also felt like, as the chairman, I should wait until I heard all of the testimony and looked all the evidence before I made any conclusions about the leadership at the agency."

Christina Elmore contributed to this story.

Cynthia Roldan can be reached at 708-5891.