Sheen has been a regular headline-grabber over the last few months with his bizarre antics, including hospitalisations, rehab and a public feud with TV bosses which eventually cost him his job on the hit sitcom.
His mother Janet, who has been married to Martin Sheen since 1961, has now spoken out to defend her son, insisting Mueller was a bad influence on him and is "only happy" when the actor is in trouble.
She also slams property tycoon Donald Trump for claiming he had warned Mueller's parents not to let their daughter marry the actor.
In an email obtained by TheDaily.com, she writes, "The Donald (sic) is spreading such vicious lies about Charlie. Is there any way to stop him? Brooke... had been to 13 rehabs before meeting Charlie. She... had such a party girl rep before she met him.
"Donald has gone on national TV twice to say Charlie brought her into this scene. Actually, he had been sober for some time before he had met her and we were convinced that she would be his downfall. She is only happy when she knows he is in trouble or miserable. She is so very sick...
"Charlie has done enough damage to himself and needs no one kicking him when he's down."
Sheen and Mueller wed in 2008 but they split after a bust-up the following year (09), which left the actor with an assault conviction.
They were recently embroiled in a custody battle over their twin sons but have since settled their differences, with Mueller agreeing to let her restraining order against the troubled star expire.