The money that was raised over the past year was at the 7-11 in Lindenhurst, but on Monday, cops say, a man stole a can with some of the money.
"It looked like he was going to make a donation to it, except he took the whole can," says Dianne.
Someone is either in desperate need of cash, or a conscience, customers say.
"I think it's a disgrace, I hope they find him," said 7-11 customer Kim Kessler.
Isabella died just five days after she was diagnosed with acute myeloid leukemia, so her mother feels very strongly that researchers need to do more about the disease.
"She has raised a significant amount of money for our annual Light the Night Walk - those funds are extremely important," adds Sara Lipsky of the Long Island Leukemia and Lymphoma Society.
It is not how much the man allegedly stole - there was about 75 dollars in the can.
"My biggest problem is that you took a can that a little girl's face is on," says Dianne, "and when you're done with the can, you're going to toss it away, so it's like tossing my daughter away."
Suffolk County Police are urging people to call Crimestoppers at 1-800-220-TIPS, if they have seen the suspect, or have any tips.
Meanwhile, Dianne's faith in humanity is already restored. While Eyewitness News was there, someone called to donate the amount stolen, and others continue to donate again and again.
If you would like to help Dianne raise money for leukemia in her daughter, Isabella's name, CLICK HERE.