Reality TV star Mueller, who is from divorced Sheen, has long suffered substance abuse problems and she checked into a drug recovery centre late last year (11) in a bid to regain her health.
She has been in and out of rehab since, and recently decided to go on a retreat for two weeks to maintain her sobriety.
Richards, who was married to Sheen before Mueller, took their twin boys, Bob and Max, into her house while their mum was away so the kids could spend time with their half-sisters.
A representative for Mueller says, "Brooke had been on a local spiritual wellness retreat for about two weeks with a couple of friends.
"She arranged for the twins and their nanny to stay with Denise and her family, so the boys could spend time with their sisters. Brooke is back home with the kids, and everyone has resumed their normal routine."