The 18-year-old leaped to his death from his Los Angeles apartment building last month after a long battle with depression. The sibling entertainers canceled performances of their "Donny & Marie" live stage show after Michael's death, but resumed work March 9.
The Las Vegas Sun said they subsequently scrapped this week's planned performances from Tuesday until at least Saturday.
"(Marie) is hanging in there, but she's struggling," Osmond's personal assistant, Darla Sperry, told the newspaper. "What can we expect? She is doing the best she can. Please keep her in your prayers."