spectralist' school, so I've just used the Romania tag.
Ritual For The Thirst Of The Earth (1968) is her most internationally-performed piece, as the choir dig into Romanian rain-ritual folklore punctuated by thunderclaps of percussion. Serenata (1974), cheekily subtitled A Little Sunshine Music, is an endearingly odd chamber work with imitated birdsong, and a final quote from Mozart performed on celeste sounding like a celestial ice cream van.
Less lighter in tone is Trommelbass (1985), with strident, scratchy strings and martial rhythms, reflecting the quest for personal and artistic freedom amidst the repressive Romanian regime of the era. Lastly, the 36-minute Requiem: Fra Angelico-Chagall-Voronet (1990, here in a 2011 recording) is a thing of wonder, interweaving texts in Latin, German, Greek, Hebrew and Romanian. Occasionally reminiscent of Ligeti, but more often taking inspiration from Byzantine liturgy and Romanian melodies, it's a great listen. I wouldn't say it necessarily sounds like Gorecki or Arvo Part, but deserves to be as well known as their work.
Ritual / Serenata / Trommelbass / Requiem