In The Book Thief, by Markus Zusak, why does Liesel Meminger tell Mr. Steiner that she kissed his son Rudy's dead body?

At the conclusion of the novel, Liesel Meminger gives her
friend Rudy Steiner, lying dead in the rubble of Himmel Street, what he never received
from her in life - a kiss. During their three years of coming of age in Nazi Germany,
Rudy's unrequited kiss represents sexuality repressed. Put another way, the teased kiss
is an affirmation of childhood innocence, and, in a time of inhumanity, underscores
Liesel's behaviour, tested but never bested: Her book-stealing isn't hardcore thievery;
her Nazi youth training leaves her untouched; when food-stealing becomes a brutal act,
she gives it up; she never hardens her heart to the sight of helpless Jews paraded
through town. But, most importantly, Liesel never consummates a sexual relationship with
Rudy, one that most certainly would have begun with a kiss. What then is the
significance of the kiss planted on the lips of the corpse of Rudy Steiner? It is the
consummation of innocence. In that one act, Liesel affirms that Innocence, not
Inhumanity, is victorious.