Sarah Darling's fiance set up a website seeking donations for Billy Ray Harris, who frequently begs on Kansas City's Country Club Plaza. By yesterday, around 6000 people had donated more than $145,000.
She said: "I think in our world we often jump to the worst conclusion, and it just makes you realise there are good people out there."
Mr Harris discovered the ring about an hour after Miss Darling dumped spare change from her coin purse into his cup.
She had taken off her ring earlier that day and put it with the coins.
Miss Darling was horrified when she realised the next day what she had done. She went back to Mr Harris and told him she might have given him something valuable.
"Was it a ring?" he recalled asking her. "And she says: 'Yeah.' And I said 'Well, I have it'."
Miss Darling said: "It seemed like a miracle. I thought for sure there was no way I would get it back."
In explaining why he did not keep the ring, Mr Harris said he had a religious upbringing. He said: "My grandfather was a reverend. He raised me from the time I was six months old and, thank the good Lord, it's a blessing."