Ko Yong-suk claims the defectors – who fled to South Korea in the 1990s – lied about her having plastic surgery and managing a secret fund.
Her lawyer says she is seeking 60 million won ($51,600) in a South Korean court.
The move is unusual – ruling family members living outside North Korea tend to avoid the public eye.
The defectors appeared on talk shows and claimed that Ko Yong-suk used plastic surgery to hide after having Kim Jong-un’s half-brother expelled from North Korea, her lawyer said.
“These defectors who often make appearances on TV are not in a position to know about her directly and what they are saying is not true,” he told Reuters.
“She and her husband find it very unpleasant.”
Ko Yong-suk took asylum in the US with her husband in 1998. She took care of Kim Jong-un when he was a teenager studying in Switzerland, according to her lawyer.
It is not clear if she will appear in court.
Ko Yong-suk’s lawyer told AFP news agency: “I’m not 100% sure, but her husband indicated she could come.”
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