Máiría Cahill, who has accused the IRA of covering up a sexual attack on her by one of its members, is favourite to become an Irish senator in a by-election.
This is despite criticisms of her past links to a dissident republican group.
Catherine McCartney, whose brother Robert was murdered by the IRA in 2005, is against her election.
She had called it an "appalling abuse of the Oireachtas (Irish Parliament)".
Miss Cahill has admitted to a very brief association with the Republican Network for Unity (RNU), a small dissident group that was formed after Sinn Féin voted to accept the PSNI in 2007.
However, despite that, Miss Cahill said she had "repeatedly stated her support for peace, for the Good Friday Agreement, and for the rule of law."
She said she was national secretary of the group in 2010, but has had no links since then and would not even describe herself as a republican any more.
She said that she left because of "outside influences", saying proof of her support for the police is that she went to them about her alleged sexual abuse.
The man accused of her rape has denied the allegations and was later acquitted in court.
Miss McCartney, who is taking civil proceedings against Miss Cahill for alleged harassment, said in a letter that has been sent to all TDs (Irish MPs) and senators that "it appears" that the Irish Labour party candidate in the Seanad by-election was associated to the RNU.
This, Miss McCartney claimed was the political wing of a dissident terrorist group until as recently as 2011.
A spokesman for the Labour party said the claims were libellous and Labour was taking legal advice.
Over the last few days, Miss Cahill has come under attack from another by-election candidate, Jerry Beades.
He said that while her account of her sex abuse was "credible", there were " too many questions " surrounding her suitability to be a member of the Oireachtas.
Miss Cahill described the attacks on her as "smears".
Mr Beades is a former property-developer and a former member of the Fianna Fáil national executive. He is standing as an independent.
The two other candidates in the by-election are Keith Swanick for Fianna Fáil and Sinn Féin's Sinead Burke.
The attacks on Ms Cahill are unlikely to have any impact on the outcome of the result, according to a Labour party source.
Because it is a Seanad by-election, only members of both houses of the Irish parliament can vote and all have already done so.
Fine Gael and Labour have a large parliamentary majority and all are expected to support Miss Cahill. The result will be announced on Friday.