Dana Rosemary Scallon will be sued unless she retracts comments she made about alleged sexual abuse within her family.
Solicitor Paul Tweed said he has also put broadcaster TV3 on notice of plans to issue libel proceedings if an apology is not issued for claims made by Dana in a televised interview last week.
Dana's niece, Susan Gorrell, who claims she was abused by another family member, has now instructed her lawyer to act.
The solicitor, from Johnsons law, said: "I have been instructed by Susan Gorrell and Susan Stein, the niece and sister respectively of Dana Rosemary Scallon, to put both TV3 and Ms Scallon on notice of our intention to issue libel proceedings unless totally unfounded and highly defamatory allegations made during the course of a broadcast on October 14 are retracted immediately."
No immediate response was available from Dana.