Linney didn't feature in the 10-minute short when it debuted as part of Britain's Comic Relief Red Nose Day telethon on Friday, but the storyline for the US version, which will air on May 25, will be completely different.
The actress' scene will be filmed in April, according to Entertainment Weekly.
"I have no idea what I'm doing yet. Not a clue," Linney says.
In the original 2003 film, Sarah was forced to give up her romance with her office crush, played by Rodrigo Santoro, to care for her mentally ill brother.
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