"But I hope the party room tells him that they very firmly believe it's a conscience issue, and he will abide by what they tell him."
She, like Mr Abbott, is a member of the Liberal Party and three years ago won a place on the Sydney City Council at the last local government elections.
Communications Minister Malcolm Turnbull went further on Tuesday, saying he fully expected parliament to legalise same-sex marriage before the end of 2015.
"I have never seen a social issue which has changed attitudes as rapidly as this one," the Communications Minister told ABC Radio.
He added, in his view, that legislation was "very likely to pass".
"If you think about, say, the British Commonwealth, if you think of the old Commonwealth, the Dominions, they are all now supporting same-sex marriage," he said.
"Australia I suppose is the odd one out or is the one that has not yet turned its mind in a parliamentary sense to reviewing the law.
"The point is the context has dramatically changed and we can't be blind to that."
The PM has declined to allow his front bench a free vote on same-sex marriage.
"Referendums are held in this country where there's a proposal to change the constitution," Mr Abbott told reporters in Brisbane.
"I don't think anyone's suggesting that the constitution needs to be changed in this respect.
"If it comes before our parliament again, our party room will deal with it, our party room will decide whether our existing policy continues or not and then we will have a good debate."
But the PM is under more pressure to allow a free vote within the Liberal Party on gay marriage by the end of the year.
The success of the referendum in Ireland to amend its constitution on the issue sparked calls for another parliamentary debate.
Assistant Education Minister Simon Birmingham said the Irish referendum was another sign to Australia there was strong public support in Western countries for gay marriage.
"When it is the right time, one of us will make sure that it is raised," Senator Birmingham said of the Liberal party room.
Liberal backbencher Wyatt Roy said he expected the issue to be raised in the party room by the end of the year.
"We could very easily have a discussion about legislation in the party room and we could have a vote in the parliament before the next election," Mr Roy told ABC Radio.
Mr Roy said he feared that if the issue dragged out into an election year it would become a political football.
"My preference is that issues like this are not turned into political footballs and it would be easier, I think, politically and better for the country if we were to deal with it this year rather than in an election year," Mr Roy said.
Mr Abbott's sister, who is openly homosexual, said she hoped her brother allowed his MPs a conscience vote.
A debate on a Greens bill could start as early as mid-June, but any vote on the issue is likely to fail until Coalition MPs are allowed a conscience vote.
Industry Minister Ian Macfarlane says while same-sex marriage isn't a front-line issue for the government, he's open to having the issue discussed in the Liberal party room.
Mr Macfarlane said he continued to oppose legalisation because that was the majority view of the people in his Queensland electorate of Groom.
Nevertheless some MPs, including from the prime minister's own back bench, are pushing for a referendum in the wake of Ireland's historic vote.
Liberal backbencher Zed Seselja says he doesn't support gay marriage, but the question should be put to the people.
Independent senator for Tasmania Jacqui Lambie doesn't support gay marriage either but backs a referendum on it.
Her fellow crossbencher Glenn Lazarus also wants the matter to go to the public and South Australian independent Nick Xenophon says he'd support a referendum if that was a "circuit breaker".
"I think the best approach is that there be a conscience vote in the parliament, after all it has been an election issue," Senator Xenophon said.
Should a bill to legalise same-sex marriage come before parliament, the coalition party room would decide whether government MPs could vote freely on the matter.
"It's up to members of parliament who are eager for change to decide whether they want to bring it forward," Mr Abbott said.
The Greens have legislation for the change already before parliament. A separate bill from Liberal Democrat David Leyonhjelm was due to be debated in March but he decided not to go ahead without coalition MPs having a conscience vote.
Under Liberal Party rules, backbenchers can vote freely but ministers must resign if they wish to cross the floor.
Labor's policy is to allow conscience votes on the issue but deputy leader Tanya Plibersek wants the party's national conference in July to bind MPs to vote in favour of gay marriage.
Opposition Leader Bill Shorten voiced his support for Ireland's move on Twitter on Saturday.
"Time for Australia and our Parliament to embrace marriage equality. Congratulations Ireland," he said.
Mr Shorten said he also believed the matter was one for parliament to resolve.
"Why is Tony Abbott stopping Australia becoming a more modern nation and why doesn't he trust his own members of his own team to exercise a conscience vote?," he said.
- Daily Mail
