Doris Schmitt left the bulk of her roughly $250,000 estate to Mr Camping, who said the world would end on May 21 2011.
In her final years, Doris Schmitt told her nieces she planned to give the massive gift to his Family Radio World Wide.
But it wasn't until last month that they realised who Camping was.
Eileen Heuwetter, 64, who was bequeathed $25,000 along with her sister, said: 'My whole family was mad and upset.'
'If it had been a cancer organisation, fine. God bless them.
'But Camping's just not a good person.'
Mrs Schmitt's life was marked by tragedy.
One of her sons died of cancer at the age of 16 and the other struggled with drugs and alcohol.
The widow from the Rosedale area of Queens turned to Family Radio for comfort, Mrs Heuwetter said.
'It became her entire life,' Mrs Heuwetter, of Jupiter, Florida, said on Friday.
Mrs Schmitt told Mrs Heuwetter she planned to give most of her estate away to the station because her closest nieces were well-off.
They initially did not object to that plan, the New York Daily News reports.
But after they learned about Camping's zany beliefs, they spoke to her lawyer who said nothing could be done.
Mrs Heuwetter said: 'It's what she wanted.' Read More