Gersdorf has said she will defy the law, which would cut short her constitutionally guaranteed six-year term that is due to end in 2020.
Meanwhile, Prime Minister Mateusz Morawiecki faced a grilling in the European Parliament for what many European lawmakers see as Poland's violations of democratic standards with a broader overhaul of the judiciary that gives the ruling party vast political control over courts and judges.
She is now married to Bohdan Zdziennicki, a retired Polish Constitutional Court judge.
The European Union has accused the Polish government of enacting laws that "interfere significantly" in the judiciary, and has given it one month to answer its concerns.
Justice Gersdorf, following through on a vow she had made, showed up for work with other justices on Wednesday morning.
Hailing from a renowned Warsaw family with deep roots in the legal profession, Gersdorf's father Miroslaw was also a respected law professor and judge.
Twenty-seven of the Supreme Court's 73 judges are affected by the new law.
"Judges are more independent now than they were in the past", Morawiecki countered.
But he noted that shifting from coal to natural gas was particularly challenging for Poland because the latter could only be sourced from Russian Federation, "so all efforts to increase our use of gas would have destabilized our security", Morawiecki said.
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Under the measures due to come into effect at midnight on Tuesday, almost 37 percent of Supreme Court judges will be forced to retire unless they are granted an extension by Duda, a PiS ally.
Chanting "We are with you!", some 5,000 protesters rallied on Tuesday evening at the Supreme Court's offices in central Warsaw in support of Gersdorf and other judges.
Their sentiments were matched by several global organizations on Wednesday including Magistrats europeens pour la democratie et les libertes, an association of European judges and the worldwide Bar Association's Human Rights Institute, who accuse Poland of ignoring the appeals of the global judicial community and subordinating judiciary to executive power.
Under the new rules, the 65-year-old judge should have asked President Andrzej Duda for an extension of her mandate if she was to be of retirement age on July 4.
In December, the European Union triggered an unprecedented disciplinary process against Poland for a "serious breach" of its values.
Dozens of people protested in front of the presidential palace Tuesday before Gersdorf's meeting with Duda.
Powerful PiS party leader Jaroslaw Kaczynski, who is widely regarded as Poland's de facto decision-maker and the mastermind behind the contested reforms told the pro-government Gazeta Polska weekly that the judges' defiance was "doomed to a disastrous defeat".
Polish Foreign Minister Jacek Czaputowicz said the law was binding and "for the time being our stance is that we are right".
In announcing its procedure, the European Commission, which polices EU law, said the measures "undermine the principle of judiciary independence".