Sharon Osbourne and her daughter Aimee have pulled out of a West End production of The Vagina Monologues "due to unavoidable personal reasons".
Sharon was due to appear in the West End from Tuesday
The family were due to return to Los Angeles on Saturday so eldest daughter Aimee, 21, could receive treatment for an undisclosed illness.
The pair, due to perform from Tuesday, apologised for "letting the cast down".
"Sharon's focus now has to be on the family and, more importantly, Aimee's health," a statement said.
Sharon and Aimee were due to take the stage at London's Wyndham Theatre on Tuesday for six weeks, in what will be the second London production of Eve Ensler's play.
The pair were treated for smoke inhalation after the fire last week
"Aimee has been taken ill and the family are therefore flying back home to LA over the weekend so that she can have further treatment and rest," the statement said.
"They hope everyone understands and would be very grateful for privacy at this sensitive and difficult time for them.
"They apologise profusely for letting the cast down and wish them all the very best for the upcoming production."
The news marks yet another slump in fortunes for the Osbourne family, who were propelled to fame in the MTV reality TV show The Osbournes.
Catalogue of woes
Last week, Black Sabbath star Ozzy Osbourne and his wife Sharon had to flee their Buckinghamshire mansion when a fire broke out while they slept.
No-one was hurt in the incident, but the British-born couple were treated for smoke inhalation, and damage to the house could run into thousands of pounds.
Last November, the couple were burgled at the same house, losing an estimated £2m-worth of jewellery.
And less than a year before - shortly after his wife's recovery from colon cancer - Ozzy suffered a near fatal quad bike crash.
Aimee is the only member of the family who chose not to appear in The Osbournes alongside siblings Jack and Kelly, claiming she disliked the publicity.
Stars who have appeared The Vagina Monologues in the past include models Jerry Hall and Sophie Dahl, comedian Jenny Eclair, TV presenter Mariella Frostrup and former Spice Girl Mel B.