02/13/2012 AT 08:00 PM EST
It was no secret that Whitney Houston
fought a longtime battle with addiction. So while her death at 48
shocked and saddened her friends and family
, as well as countless fans, the news wasn't exactly out of the blue.
"As sad as this sounds, it's not a great surprise and yet, it's unbelievable," a music source tells PEOPLE. Houston herself had admitted her drugs of choice were cocaine and marijuana while reports are now emerging that there were prescription pills found in the hotel room where she died.
"There are demons she fought privately and publicly for many years," the source continues.
"While doing [the upcoming feature film
she was seemingly in a good place but the demons run deep. Very deep."
Adding danger to her demons, says the source, were Houston's enablers.
"She's been on a downward spiral for a long time and when you have those people around you that enable the behavior ... she couldn't shake those demons."
The singer's cause of death has been deemed inconclusive
by the L.A. coroner. Her body was found in the bathtub
of her Beverly Hilton hotel room just hours before she was set to attend Clive Davis's pre-Grammy bash