In 1631, she accompanied the queen, Maria Eleonora of Brandenburg, to Germany, where she joined her second spouse Horn who served in the Thirty Years' War.
Accordingly, in 1639 Ebba Leijonhufvud and Christina Natt och Dag was appointed to share the position of royal governess and foster mother with the title Upptuktelse-Förestånderska ('Castigation Mistress'), while Beata Oxenstierna and Ebba Ryning was appointed to share the position of head lady-in-waiting, all four with the formal rank and title of Hovmastarinna.
The choice of Ebba Leijonhufvud and Christina Natt och Dag to the office of foster mother was officially motivated by their mutually reputed qualities of "honesty and virtue, seriousness and steadfastness",[3] and in the case of Leijonhufvud in particular, her ideally educated daughter Anna Margareta was noted as an example of the great ability of her mother in raising a child.
[3] Christina Natt och Dag for her part had good connections at court, her paternal grandmother Karin Gyllenstierna having been the chief lady-in-waiting to queen Catherine Jagiellon and princess Anna Vasa of Sweden.
With some exceptions, such as Ebba Sparre, lady Jane Ruthven and Louise van der Nooth, Christina did not show any interest in any her female courtiers whatsoever, and she generally mentions them in her memoirs only to compare herself favorably toward them by referring to herself as more masculine than them.