Mueller, 33, has checked into a sober living facility, her mother, Moira Fiore, tells PEOPLE.
"She is struggling with her sobriety and we are going away on a cruise so we feel better that she will be there while we are gone," says Fiore, who adds that Mueller is expected to remain at the facility for about two weeks.
While Fiore did not reveal the name of the center, she says, "It is a facility for very wealthy people trying to fight addictions. Brooke is really trying to get her life back."
Last month, Sheen filed for divorce from Mueller, with whom he has 1 ½-year-old twin boys.
Mueller has been working on a new reality show with Paris Hilton, and earlier this week they showed up at Las Palmas in Hollywood riding in Hilton's pink Bentley and being filmed by a camera crew.
"Paris and the other girls on the show are going to Las Vegas and Brooke did not feel she could handle it now," says her mother. "She was scared. We're all happy she will be in the facility and hope she will feel better."
Earlier this year, Mueller spent time at The Canyon rehab center in Malibu.