The 39-year-old former wife of Charlie Sheen is seeking treatment after a recent incident in which she was found walking barefoot and looking confused near a bar in Salt Lake City in Utah with her and Charlie's children, seven-year-old Bob and Max.
Brooke's sister, Sydney Wolofsky, told Entertainment Tonight: "She was in the hospital for a little bit. I do know she woke up in the hospital after detox and my mom asked her what she wanted to do at this point, and she was the one that said, 'I want to go back into rehab, and I want to stay there for a while.'
"It was definitely her decision [to go to rehab]."
Brooke's mother, Moira Fiore is now looking after the twins, "so their daily routine stays the same while Mueller is in treatment for abusing prescription drugs".
And her family are planning to spend time with Brooke over the festive season.
Her sister added: "I know that we're going to see her on Christmas. We're going to go over [to the rehab facility] to visit and just spend time with her. My brother, his wife and two kids, my parents and I are going to go to Utah to spend Christmas with her. Brooke would not let us show up without the boys.
"We send her pictures and videos of them all the time. Her whole life revolves around the boys, [who are] looking forward to seeing her. They miss her and really love her. They know what's going on, and that mom's getting help."