Mercedes was jilted by fiancé Riley Costello (Rob Norbury) last year after she confessed to her affair with his dad Carl (Paul Opacic). She was then held captive by serial killer Silas Blissett (Jeff Rawle).
Since letting Riley leave the village with their baby son Bobby, Mercedes has faced temptation after Doctor Browning offered her money to sleep with him.
Metcalfe told OK Extra of the new storyline: "It was refreshing and brilliant to go back to how Mercedes was when I first joined the show. It was good to put the Silas kidnap storyline and everything else that's happened behind her, but there are still moments where she flicks back to being quite depressed."
"The sky's the limit for her," she continued. "Whatever she does that's bad, she manages to justify in her head. She doesn't have much self-worth and she knows what she's like."
The 28-year-old added that she is pleased Mercedes did not secure a stable future with Riley and their young son.
Metcalfe said: "She's tried but it's just not her. She's at her best when she's free and single, so I wish she would be happy just doing that. It would have been nice if she'd settled down with Riley, but being nice is really boring! I like her the way she is."
Hollyoaks airs weeknights at 6.30pm on Channel 4 with a first look screening at 7pm on E4.
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