Jett Travolta, who reportedly had suffered health problems for most of his life, died of a seizure disorder last week at the age of 16.
Some Scientology critics have speculated his parents didn't get him proper medical care due to their beliefs.
"Folks, as popular as it has been to discriminate and ridicule Scientology and Scientologists in the recent past, now is not the time," Usmagazine.com quoted Presley as saying on her MySpace blog. "It is not true that Scientologists 'don't believe in' medical care, medicine or medical doctors and that may have something to do with this terrible tragedy. Just like anyone else, if one is sick, they go to the doctor. If a medication will make it better, then they take it. If they don't, then they are an idiot, and you can't blame their religion. Whatever medical and or physical condition Jett had, I can tell you first-hand that his parents were on a tireless, never-ending quest to get and provide him with the absolute best care anyone could ever ask for and need -- medically, physically, emotionally, medicinally and spiritually."
She added that she wasn't taking to the Internet to preach her beliefs.
"I am here to protect my friends," she said. "Please let this family grieve in peace."
People.com said a memorial service is planned for Jett Thursday in Ocala, Fla., where the family has a home.