Frances Bean, 21, lost her famous father, the Nirvana frontman, to suicide when she was 19 months old.
Her words to Williams were among thousands of sympathy messages the 25-year-old daughter of the comedian and Oscar-winning actor received after his death in a suspected suicide.
Williams also received some hateful messages, leading to her declaration that she was abandoning social media for a while.
"I'm sorry. I should've risen above. Deleting this from my devices for a good long time, maybe forever. Time will tell. Goodbye," she wrote in a final Twitter message earlier today.
Before quitting Twitter and Instagram, Williams posted a touching tribute to her iconic father, star of "Mrs. Doubtfire," "Good Will Hunting" and Disney's "Aladdin."
Quoting a passage from French writer Antoine De Saint-Exupery's "The Little Prince," Williams wrote, "I love you. I miss you. I'll try to keep looking up."