Exiled to Florence with her family, 1634–43,[2] Marie (whom the French knew as "Mademoiselle de Guise") became close to the Medicis and came to love Italy and especially Italian music.

For over forty years scarcely a week passed that she did not write to her Medici friends in Florence, or receive word from them through the Tuscan resident in Paris.

[4] The old stable wing that stretched along the garden was also renovated and subdivided into comfortable apartments to be occupied by what might be likened to today's artists and intellectuals in residence: Philippe Goibaut, Roger de Gaignières, and, a bit later, Marc-Antoine Charpentier.

Mlle de Guise protected him and advanced his career by soliciting commissions from people or establishments who were seeking her continued patronage.

With the help of Father Nicolas Barré, Minim, she founded a teachers' training institute and created schools for girls and hospitals for the poor in her Parisian parish and in her provincial lands.

In her vast Parisian residence known as the "Hôtel de Guise," she presided "magnificently" over a select little "court" composed chiefly of members of the House of Lorraine, clergy, learned protégés, and Italians passing through Paris.

In the early 1670s, Marie had begun to assemble a small ensemble of household musicians to perform pieces by a variety of French and Italian composers, among them Marc-Antoine Charpentier.