The actress, who played Sharon Theodopolopoudos for nine years, also made a guest appearance in ITV cop drama The Bill last September.
A spokeswoman for the show told DS: "We are thrilled that Pauline will be part of an upcoming episode of Casualty.
"Pauline will be playing a homeless person who ends up getting trapped within an internet cafe and suffers horrific injuries."
The dramatic scenes will be shown in mid-October when Casualty enters its 20th anniversary year.
