Brooke Mueller checked herself back into a rehabilitation facility last weekend after fearing she would slip in her battle for sobriety by flying to Las Vegas to party with Paris Hilton, according to her mother.

Charlie Sheen's estranged wife first sought treatment for personal issues in February, following her bust-up with the actor in Aspen, Colo., last Christmas.

She admitted herself into another sober living center in Los Angeles on Saturday and is expected to remain there for two weeks as she continues to stay clean.

And Mueller's mom, Moira Fiore, reveals a planned vacation with pal Hilton prompted her daughter to seek further help because she was "scared" she would lose her grip on her sobriety.

Fiore tells People magazine, "Brooke is struggling with sobriety, and we are going away on a cruise, so we feel better that she will be there while we are gone.

"Paris and the other girls were going to Las Vegas, and Brooke did not feel she could handle it; she was scared. Brooke is really trying to get her life back."