If you are looking for a "partitura" (sheet music) for piano and voice, several reliable platforms offer high-quality arrangements:

Composed by with lyrics by Félix Luna , the song was first popularized by Mercedes Sosa in 1969. It dramatizes the final moments of Storni, who tragically took her own life in 1938 at La Perla beach in Mar del Plata after a long battle with breast cancer and depression. The lyrics poignantly describe her "walking into the sea" to sleep among the corals and sirens. Finding and Using the Partitura

To get a high-quality PDF for your project, consider these sources:

Alfonsina y el mar Sheet Music for Piano (Solo) - MuseScore.com