Credit: Tibrina Hobson/

Prayers for Bobbi Kristina.

As the only child of the late Whitney Houston and Bobbi Brown reels from her mother's sudden Feb. 11 death, her family members -- including maternal grandmother Cissy Houston and cousin Dionne Warwick-- are gravely concerned for the 18-year-old aspiring singer.

Multiple sources tell the new Us Weekly that the aspiring singer -- who watched both of her parents struggle with substance abuse -- has turned to drugs, and her loved ones are urging her to go to rehab.

"Whitney's passing is sending Bobbi off the deep end," one insider says, adding that her family is "shocked" by the scope of her issues. 

"Bobbi's problems are out of control," the insider notes.

For more on Bobbi Kristina's new struggle -- her blowout fights with her famous mother, her family's plans to find help -- pick up the new Us Weekly, on stands Friday.