Is a Muslim female student who organizes a university party where alcohol is served sinful, knowing that her role does not include direct handling of alcohol?

It is impermissible to serve or introduce alcohol into activities and parties, because doing so exposes the perpetrator to the curse of Allah Almighty; as the Prophet, peace and blessings be upon him, said: "Allah has cursed alcohol, its drinker, its server, its seller, its buyer, its presser, the one for whom it is pressed, its carrier, and the one to whom it is carried."

It was obligatory not to accept the serving of alcohol or to resign from a responsibility that involves it. The expiation for what you have fallen into is sincere repentance, a firm resolve not to return to it, and drawing closer to Allah through righteous deeds.