。
She led a group of nuns known as the Missionaries of Charity.
Literal
She [topic-は] Missionaries-of-Charity [quotative-と] called nuns [possessive-の] group [object-を] was-leading.
This sentence almost certainly refers to Mother Teresa, who founded the 神の愛の宣教者会 ('Missionaries of Charity') in 1950 and led it until her death. Note: the source spells the name 慈善伝導団, but standard usage spells it 慈善伝道団 — 伝道 ('missionary work') is the correct compound (using 道 'way / path'); 伝導 means 'conduction (of heat, electricity).' This is most likely a typo. The pattern X と呼ばれる Y ('Y called X') uses the quotative と with the passive 呼ばれる to embed a name as a modifier. 修道女 ('nun') = 修道 ('religious training') + 女 ('woman'); 達 is the plural marker.