Mueller, 35 is in the Betty Ford clinic for a 30-day stint, reported Radar online.
"Brooke and Lindsay are currently staying in the hospital wing at The Betty Ford Center in Rancho Mirage. In fact we're told that they've already run into each other and exchanged pleasantries," a source said.
The 35-year-old mother of Sheen's twin boys Bob and Max might not not receive custody of the boys back when she will be out.
The boys are currently cared for by Sheen's other ex-wife Denise Richards, who is slated to attend a hearing in child dependency court early next month .