She briefly served as Serbia's minister of health in the transitional government that was established after the fall of Slobodan Milošević's administration in 2000.

[2] The party contested the 1992 Serbian parliamentary election as part of the Democratic Movement of Serbia (DEPOS) alliance, and Kostić received the twenty-fourth position on its electoral list in Belgrade.

The party received the ministry of health in the new coalition government, and Kostić was appointed as minister on October 24, 2000.

[11] In January 2001, Kostić indicated that the ministry of health would appoint a commission of scientists and doctors to monitor the possible long-term effects on the Serbian population of depleted uranium munitions fired by North Atlantic Treaty Organization (NATO) forces in the 1999 NATO bombing of Yugoslavia.

After the election, the Democratic Party of Serbia nominated Obren Joksimović to replace Kostić as health minister.

Joksimović's nomination was criticized by many in the health sector; a group of doctors in Požarevac referred to him as unsuited for the role while describing Kostić as "the kind of person whose professional and ethical qualities fully suit a ministerial role, something that she has demonstrated in the work in the Serbian interim government and in her public appearances so far.

Kostić returned to political life in 2016, appearing in the eighteenth position on electoral list of the Enough Is Enough (Dosta je bilo, DJB) movement in the 2016 Serbian parliamentary election.

[23] In March 2018, DJB delegate Miloš Bošković announced his resignation from the assembly; Kostić was the next candidate on the movement's list eligible to receive a mandate.

She indicated that her decision was made partly for practical reasons, as she had limited opportunities to engage in parliamentary activities as an independent member.

[29] In May 2020, Kostić presented conspiracy theories related to the COVID-19 pandemic that involved, among other things, the 5G network, Bill Gates, George Soros, and an opposition to vaccination.