Doman added that she hoped now "he's eating oatmeal" in jail.
She knew Peterson's arrest was coming because she had been working with authorities, and she hoped justice would finally be done.
May 13 would have been Kathleen Savio's 46th birthday, her sister noted. Every year, she said, family members visit her grave and relive the pain of her death. This year, she added, there will be some relief.
Savio's divorce from Peterson was nearly complete at the time of her death. She had received an order of protection in 2002 against Peterson, alleging a pattern of physical abuse and threats.
Doman said she wants to encourage battered women to get out of bad relationships, claiming Drew Peterson battered her sister.
"No matter how strong you are, get out," she said she would tell other abused women.
A lawyer for the Savio family, Martin Glink, told ABCNews.com the family is "very grateful and relieved that at long last he [Drew Peterson] is going to be charged.
"We're hoping that Mr. Peterson will get a measure of justice," Glink added. "We're looking to have the right thing done and that obviously points to Drew Peterson."
Stacy Peterson, then 23, vanished Oct. 28, 2007, after reportedly telling her minister that Peterson had confessed to killing Savio.
Earlier this year, a grand jury was convened to decide whether to indict Drew Peterson for Stacy Peterson's disappearance, but it has not done so. Like Savio, Stacy Peterson told family and friends that she feared her husband.
Drew Peterson has maintained that Stacy Peterson ran away with another man.
In November 2007, when the state announced it wanted to reopen Savio's case, Peterson told ABC News that he would put more investigative stock in the first determination that Savio's death was an accident.
"I put more faith in the first autopsy because it was fresh," he said at the time.
ABC News' Martin Bashir, Elizabeth Tribolet, Jesus Ayala, Lindsay Goldwert, David Schoetz, Barbara Pinto and The Associated Press contributed to this report.