It's just the valor of surviving Order 66, somehow, impossibly getting away, and yet still coming back into her gutted home-turned-tomb to do this excruciating, ultimate act of sacrifice. Destroying this last physical manifestation of her people's culture, identity, and her own life's work. It's such a Jedi moment: letting something deeply important go, not out of apathy or coldness, but to protect others.
Jocasta as a character is so defined by her exchange in AotC, telling Obi-Wan that if something isn't in the Jedi Archives, it doesn't exist. So many fans have interpreted that as to stand for the arrogance of the Jedi, not the pride in her life's work collecting and maintaining a resource as incredible and massive as the Jedi Archives. I think this act is even more powerful answer to those charges; far from Jocasta Nu being a posterchild for the Jedi doggedly clinging to an institution for the sake of itself, she's willing to throw all of that away in an instant if it means one less weapon for the Empire.