At first I could not figure out who the letters were from, but after deciphering many clues within them, I have concluded that they are from Adèle de Rougemont, daughter of Frédéric de Rougement a contemporary of Henri's father and author of over 50 books on Geography, Ethnography and Theology.
Natalie de Freudenreich
Château de Monnaz
A passage from one letter seems to indicate that Natalie and Henri were a great match and both cared deeply about those less fortunate.
“That the most gracious God blesses you abundantly, and allows you to do all the good that you wish around the ancient manor. It's true the times of the troubadours have passed. No passing minstrel will immortalize a song of love to you beneath it’s windows. Hopefully in exchange however, you will hear the joyous voices of poor children, who will celebrate the goodness of their young lady of the manor. The de Büren’s of Vaumarcus are well known in the area for their generosity towards the poor and Mr de Büren was very wise to choose you to become a partner in his charitable works. He could not have found a more compatible mate in caring about orphaned children or the miseries endured by the sick.“
While these indications of Henri's charity are eight years after his return from his voyage to the Americas, the roots of his empathy are present during his voyage. As a case in point he lauds a school for orphans, Girard College in Philadelphia as "the most beautiful building ever erected in the name of charity."