Genshin dropping Madame Ping's lore in an event was absolutely vile like how dare they just give us the most heart-wrenchingly tragic sapphic rivalry. An inventor and an artist constantly arguing and Xianyun dragging Zhongli into it to mediate. They soon grow closer and one day Guizhong dies so suddenly and horrifically it makes Madame Ping rethink her ideas of immortality and death and descend to the human realm.
All she carries with her is a bell, made by Guizhong, a bell she previously viewed as unable to depict the soul in the way human-made music could. But it's not that anymore. In the way Madame Ping depicts the soul through music, Guizhong depicted it through creation. That bell carried Guizhong's soul, a soul she entwined with Madame Pings. That's why Zhongli gave it back to her when Madame Ping left for the mortal world.
When Zhongli requests the bell for his funeral, it carries so much more weight. He isn't just requesting a ceremonial bell, he's requesting Guizhong's soul and love, he's requesting a mourner who departed far earlier than him. He's also requesting a blessing from Madame Ping, to live as a human.
Madame Ping takes the appearance of an elderly woman, somebody who is weary and full of wisdom. She has lived lifetimes and she shows it in her form. She mentors young creators around her, Xiangling, Yanfei, Yaoyao and the like. She gives the Traveler a teapot, so they have a place to call home for a little while. She cares for the glaze lillies, because they are the scattered notes of the torn sheet music that's Guizhong's love for humanity. She doesn't play music anymore, because the only one who could hope to understand her tune, the one attuned to her soul, is gone.
Her last song was to mourn Guizhong because grief is love with nowhere to go. She put it in music created with callused hands, like Guizhong's making of the bell. She played for a lantern, a love, a ghost.