"You – you alone will have the stars as no one else has them," the 25-year-old wrote on Twitter, quoting the 1943 classic of children's literature.
"In one of the stars I shall be living. In one of them I shall be laughing. And so it will be as if all the stars were laughing, when you look at the sky at night."
In her own words, Zelda added: "I love you. I miss you. I'll try to keep looking up."
In 2011, Robin and Zelda collaborated on a video for Nintendo about the origin of her name. "It's magical," Robin explained. "As she is."
Williams's final Instagram post was a vintage picture of the two of them, father and daughter, posted to celebrate Zelda's birthday on July 31.
"Quarter of a century old but always my baby girl," he wrote.
If you or someone you know is considering suicide, please contact the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).