Victims campaigner Ann Travers said she was overwhelmed after SDLP grandee Seamus Mallon accused the party of giving "two fingers" to unionists by threatening to block laws preventing former criminals being given senior Stormont posts.
The former Deputy First Minister said the public perception was that people are being rewarded for violence and urged the party to change its mind.
The SDLP Assembly group meets today to make a final decision on the issue following an emotional face-to-face meeting with Ms Travers last week.
Mr Mallon, a former SDLP deputy leader, said the symbolism of appointing advisers with criminal records was akin to saying: "Don't take us seriously when it comes to relations with the unionist community because we are going to reward violence."
He added: "I hope the party changes its mind and I will do my best to ensure that they do.
"In politics, when you are explaining, you are losing."
Ms Travers, who has warned the SDLP could lose support over its stance on the issue, said Mr Mallon's contribution was "superb and fantastic".
She said on Twitter she "really could not ask for much more" and was "overwhelmed".
Ms Travers began her protest after a member of the IRA gang which shot dead her sister Mary as she left Mass with her family in 1984 was appointed as a Stormont special adviser, or 'spad'.
The appointment of Mary McArdle as a spad to Sinn Fein Culture Minister Caral Ni Chuilin led to TUV leader Jim Allister's Private Member's Bill, which would stop those with serious convictions being appointed.
The SDLP has threatened to block the Bill using a veto that would require a majority of both unionists and nationalists.