Edith Windsor's case is one of several challenges winding their way through US courts for possible supreme court hearing

An 83-year-old marriage equality campaigner was at New York's federal appeals court on Thursday for the latest stage of her fight against a federal act that defines marriage as between a man and a woman.

Lawyers for Edith Windsor argued that her marriage to Thea Spyer, in 2007, should offer the same federal rights as a union between a man and a woman.

Windsor's legal team say the 1996 Defense of Marriage Act (Doma) discriminates against her and others by limiting marriage to heterosexual couples. Thursday's hearing was the latest in many legal battles for same-sex equality across the United States; supporters ultimately hope a supreme court ruling will overturn the law.

Windsor, a former IT worker, met Spyer in 1965. They became engaged in 1967 and finally married in Toronto in 2007. Spyer died in 2009 after battling multiple sclerosis for many years, but, unlike opposite-sex married couples, Windsor was not entitled to any tax relief on her inheritance. Windsor had to pay $363,000 in federal estate taxes.

"The Defense of Marriage act discriminates against gay people," she said outside New York's second circuit court of appeals. "Not only is it illegal, as my lawyers argued today, but it refutes, it really challenges the basic principles on which this country was founded: fairness and equality."

Windsor and her supporters say current federal law violates the 14th amendment of the US constitution, which guarantees equal protection under the law. The Obama administration said in 2011 it considered Doma unconstitutional and would no longer defend it.

The American Civil Liberties Union filed the case on behalf of Windsor earlier this year, and in June a federal district judge in New York ruled in her favour. But House speaker John Boehner convened what became known as the Bipartisan Legal Advisory Group to defend Doma in court after Obama withdrew his administration's support. Boehner's group appealed the district judge's verdict on Windsor, prompting Thursday's hearing.

The second circuit court expedited the case due to Windsor's age and poor health – she told the Guardian she had "a number of major illnesses" – while Windsor has also asked the supreme court to review her case. Federal courts in Massachusetts, California and Connecticut have previously found the law unconstitutional, and those cases are pending before the supreme court, which has until Monday to decide whether to take up the issue in its next term.

"In the last few years virtually every case that has addressed the issue has struck down Doma," said Windsor's lawyer, Roberta Kaplan. She said she was confident the judges would find in Windsor's favour but would not be drawn on how long that might take.

The justice department has filed petitions in all four cases, asking the high court to review the constitutionality of the law's definition of marriage. A lawyer for the department was in court on Thursday, essentially providing evidence in support of Windsor's case.

Also present in the packed courtroom were various supporters of Windsor, some of whom were embroiled in their own legal battles elsewhere. Joanne Pederson, who is bringing her own Doma challenge in Connecticut, was in court with her wife, Ann Meitzen, to "show our support for Edie".

Pederson, who held a civilian position in the US navy for 30 years, says she cannot add Meitzen, who has health problems, to her health insurance plan because of Doma. "Just because we're a same-sex couple, it shouldn't mean we don't receive life benefits," she said.

It is likely to be several weeks before a ruling on Windsor's case in the second circuit court. Any supreme court verdict would not likely come before the election."I look forward to the day when federal government recognises all marriages as legal, and I'm very hopeful that that day will come while I'm still alive," Windsor said on Thursday.

"I know my spouse Thea, who shared my life for over 40 years, is here in spirit, and I'm sure she's very proud that we've got this far."

© Guardian News and Media 2012

[Image by Michael Hehet on Flickr, Creative Commons licensed]