Mueller's lawyer, Yale Galanter, told E! News his client has been in in-patient rehabilitation for close to three weeks, but she never suffered a relapse of her drug addiction.
"When Brooke did her final sentencing [May 22], she did it by phone because she was in rehab at the time. This was all discussed in open court," he said. "This [rehab] was a pre-planned event."
"This process began when she entered in December and now this is part of her after-care program. Her overall treatment plan was always contemplated to be a year. She goes back every once in a while for what I call tuneups or maintenance," Galanter added. "Otherwise, she is doing fine ... [she] has to pee in a cup three or four days a week."
Galanter dispelled rumors the former "Two and a Half Men" actor was involved with Mueller's return to rehab. In fact, he said, the former couple, who have twin sons together, are doing "really well" and "are very close."
"I am speaking out because Charlie and Brooke and everyone just couldn't stand the rumors anymore. Charlie has nothing to do with her being in rehab again," Galanter said.