It has been announced that Kim Medcalf is to return to Albert Square in the role, first played by Westbrook in 1990, but also previously played by Medcalf between 2002 and 2005.
Westbrook tweeted: "Wishing kym [sp] the best of luck at @BBCEastenders yet again this poor woman has to recreate a Samantha Mitchell as close to my last two recent come backs on the square go smash it darling.
"Oh but not to @bbceastenders my legal team will be in touch."
The 48-year-old actor and reality TV star also wrote on Twitter: "Well well well who knew... all I can say is thanks looks like I dodged a bullet."
And she added: "Bet you all can’t wait for my new book now can ya ….. oh it’s gonna go way back to the things I’ve never ever told #beafraidpeople #itsallgood."
Westbrook made her name playing Sam Mitchell as a teenager in the BBC soap. The daughter of Peggy Mitchell and the younger sister of Phil and Grant Mitchell, she worked as a barmaid in The Queen Vic pub.
Westbrook's contract was terminated in 1996 and the star has since spoken publicly about her on-an-off battles with drug addiction.
When EastEnders wanted to bring back the character of Sam but Westbrook was unable to play her, Medcalf was cast in the role.
But in 2009 the part was written back into the BBC soap for two brief stints and Westbrook was invited to return to Albert Square.
She also appeared in 2016 for the funeral of her mother Peggy, played by the late Barbara Windsor.
Medcalf, 48, has said of her return: “When the BBC approached me last year to reprise the role of Sam I was thrilled.
“She’s a brilliant character and I can’t wait to get back in the Square this spring and work with the amazing cast of both familiar and new faces.”
In February 2019 she appeared on ITV's The Jeremy Kyle Show to discuss her drink and cocaine addiction.
She admitted: "If I had the money I would be back doing 11 bags a day."
Westbrook famously suffered damage to her nasal septum as a result of past cocaine abuse and has also previously said that a botched surgery left her with osteoporosis which is making the bones in her face weaken.
Last year, the actor announced that she was having work done to “rebuild” her face and she has now said she is ready for the future and to get working again.
In 2018 she was diagnosed with womb cancer, but was given the all clear by doctors in April 2019.
Watch: The latest soap news from Albert Square