The star, who plays Ronnie Mitchell, posted a snap of herself with on-screen sister Roxie Mitchell, played by Rita Simons, to her Twitter feed.
Samantha tweeted "Back together again #mitchellsisters @OfficialRita" with the photo, while Rita replied "Woohoo! #bigsis x".
Ronnie exited the show in 2011 after a gruelling storyline that saw her swap her own cot death baby for Alfie and Kat Moon's (Shane Richie and Jessie Wallace) child, leaving them to believe their son had died.
At the time Sam told Hello! magazine: "I worked out I'd been crying or screaming at work every day for six days a week for over two years. Can you imagine how exhausting and tiring that is? You're crying, weeping and telling your brain something awful has happened, so of course that is going to affect you and your body. My brain may know I am acting, but my body was doing a different thing. I needed to stop and find some peace, a bit like Ronnie."
Samantha's character has been in jail on the soap for the past two years after her crime was uncovered.
Of her return she said: "I am thrilled to be returning to the role of Ronnie for the next six months. Ronnie is coming out of prison and her re-appearance in the Square is going to create havoc. I can't wait to be a Mitchell once again."