"She needed to get away and just take care of her own demons in her own mind and begin this process of repairing," he tells Entertainment Tonight in an interview scheduled to air Wednesday. "Marie is a strong woman but she's going to collapse – and she did."
Osmond's son, Michael Bryan, died on Feb. 26 after jumping from the balcony of his Los Angeles apartment. Since his death, Osmond and her brother have returned to the stage, performing their Las Vegas variety show.
And according to Donny, 52, his sister's tireless work ethic is helping her get through the pain.
"Our dressing rooms are right next door to each other," he says. "I can hear her crying and that hurts. What's amazing is that just minutes after she's cried, she'll come out of the dressing room, perfect and ready to go."
"She has her moments," he continues. "I admire her and I'm so glad she had The Donny and Marie Show and QVC and all these other things that kept her busy … She's been able to pick herself up and survive."