Most of the “good” websites devoted to Gemma are (naturally) in Italian. If you are fluent in Italian, or wish to weed through Google’s sloppy translation of these pages, then there are several.
Most of the available information about Gemma in English is standard and tends to get redundant. Again, most of the thoughtful analyses concerning her spirituality are in Italian. Only a handful of her writings have been translated from Italian into English. Most of her letters, diaries, and ecstasies remain untranslated – and it seems that the English-speaking Italians are in no hurry to make these materials available. (Not a good enough market for it, I suppose.)
Of the available materials published in English, allow me to recommend:
“The Life of Saint Gemma Galgani” by Venerable Father Germanus Stanislaus, C.P. (
tanbooks.com/index.php/page/shop:flypage/product_id/572/)
“The Autobiography of St Gemma Galgani” which can be viewed here:
stgemmagalgani.com/2008/11/autobiography-of-saint-gemma-galgani.html (or if you would like an actual physical copy, then I might could obtain one for you from the Passionist Nuns based in Kentucky)
“The Voices of St Gemma Galgani: The Life and Afterlife of a Modern Saint” by Rudolph M. Bell and Cristina Mazzoni. (This book includes a translated copy of the autobiography in addition to several excerpts from her diaries and letters.)
and, finally, this
link which includes a few other published letters from Gemma to Fr. Germanus, her spiritual director.