"When she heard about the tragedy, she was a mess. She was in disbelief," says the friend.
Michael, 18, took his own life on Friday night in Los Angeles. The Osmond family has gathered in Las Vegas, where Donny and Marie's show is on hold indefinitely, to mourn together.
"They're doing the best they can," the friend says. "They're all together. She's taking care of her family. They're all trying to explain that certain [bad] things happen while they grieve at the same time. They're trying to understand and make sense of it."