The New York Post said the jury announced its guilty verdict Tuesday after four hours of deliberations.
Although Lowery, Stein's former personal assistant, was convicted of murder and embezzlement in the case, Lowery's family maintains she is innocent.
"This is the kind of case that will be back. We are preparing an appeal," the Post quoted Lowery's stepfather Daniel Walsh as saying after the verdict was read.
Lowery is scheduled to be sentenced March 22. She faces a maximum of 25 years to life in prison, the Post said.
She was convicted of second-degree murder and 20 counts of stealing $30,000 from Stein, the Daily News reported.
Prosecutors said the theft sparked a brutal confrontation that led to Stein's death at the age of 62 in her Manhattan apartment Oct. 30, 2007.