If you can read Portuguese--or if you believe Google translator--then I can wholeheartedly suggest reading the latest entry in Vítor Marceneiro's blog, this one about Maria Teresa de Noronha, written by one of the great, great guitarists--Raul Nery--who played for her for many years. Near the end he says "Ela e a Amália são as maiores fadistas. E não posso dizer que uma seja melhor que a outra." That is, "She and Amália were the greatest female fado singer. And I cannot say that one was greater than the other."
There is so, so little written about her, that to hear something coming from Raul Nery really is a wonderful surprise. link to the post