Her grandmother was so heartbroken, she sold her home to give her $100,000 for chemotherapy.

Her dad cleaned out his IRA to donate $25,000.

Authorities yesterday laid out the alleged lies of a diabolical Long Island junkie who they said pretended to have bone, brain and other cancers to fool her family and strangers into sending her money for “treatment.”

Brittany Ozarowski, 21, of Medford, spread her sob story on Facebook— and then collected a six-figure windfall to fuel her heroin habit, officials said yesterday.

She was arrested Monday and slapped with a grand-larceny rap.

“This defendant perpetrated an absolutely despicable scam,” said Suffolk DA Thomas Spota. “There was no cancer, no chemotherapy, no radiation, and no medical bills. There was just heroin.”

Ozarowski’s drug-money mania knew no bounds. The addict zeroed in on a Smithtown man who lost his own son to cancer in 2007 and founded a charity in his name to help others with the disease.

“Her story was so compelling,” said Walter Warren, who lost his 19-year-old son, Kenny, to lymphoma in 2007. “I got very emotional when I met her, because it brought back a lot of really tough memories. I wanted to help.”

Warren took part in several fund-raisers — including a dinner dance and a charity dog-grooming — that raised thousands of dollars for treatment of Ozarowski’s nonexistent illness.

Ozarowski placed donation jars with a picture of herself in a wheelchair at 25 businesses and periodically collected her earnings. She also created a Web site that used the same photo.

Kindhearted donors became suspicious of Ozarowski’s story when she refused to accept rides to the doctor, and claimed that a new vitamin allowed her to keep her hair despite relentless chemotherapy sessions. They called cops, who surveilled Ozarowski for months, and arrested her in front of a Sayville supermarket while she passed out fliers.

Ozarowski has been living in a Medford motel with her father, Thomas McDermott. He told cops that he forked over $25,000 in retirement savings to help her.

Ozarowski’s grandmother sold her Selden home several months ago and gave her $100,000 to pay for phantom treatments at Memorial Sloan-Kettering Hospital, according to the DA.

“This is devastating,” said Liz Petracola, a pet-grooming store owner who organized a benefit for Ozarowski last September that raised $3,000. “I have breast cancer. When you have people out there that really need money, it just makes what she did so much worse.”

Ozarowski, whose lawyer did not return calls, is scheduled to be arraigned today in Central Islip.