Born in Rome in a family of Pugliese origins (her parents were from Foggia), she graduated in Classics from La Sapienza University in 1948, tutored by Byzantinist Silvio Giuseppe Mercati.
She obtained habilitation ("libera docenza") in Byzantine philology in 1960 and in Greek Paleography in the following year, and became Professor of Greek Paleography at the Scuola Speciale per Archivisti e Bibliotecari (connected to La Sapienza) from 1961 to 1975.
In 1976 she applied for the Chairs of Byzantine Philology and Greek Paleography at La Sapienza, winning both; she chose to hold the former, teaching the latter per assignment.
[3] She studied and critically edited homiletic, hagiographic, and religious Byzantine texts, both in prose and in verses.
German Byzantinist Vera von Falkenhausen pointed out that more than half of Follieri's works deal with hagiographic matters, but if one considers all the specific passages about hagiography, the percentage raises up to 95%.