Last month, it emerged that Kirsty will deliberately cause a nasty injury to Fiz's hand at Underworld as she is fed up with her interference when it comes to Tyrone Dobbs.
When Fiz's machine breaks at the factory and she tries to fix it, she ends up getting her hand trapped after Kirsty (Natalie Gumede) secretly switches the power back on.
At first, Kirsty pretends to be concerned for Fiz and even heads to hospital with her, but she later makes it obvious that she was responsible.
McAlpine, confirming the storyline, told What's On TV: "Kirsty continues to look after Fiz and stays with her while she is treated at the hospital and even returns home with her. She is quite sinister and when she finally leaves, Fiz is quite shaken by Kirsty's behaviour.
"Fiz has now seen how scary Kirsty can be with her own eyes. Fiz is not soft, she has spent time in prison before, but she has now seen what Tyrone has to cope with when Kirsty gets angry."
She added: "Fiz really cares about Tyrone. Fiz is also very stubborn and has a sense of justice. She will probably want to see this through to the end - she wants the truth to come out. She wants Tyrone to be happy and feels this can never be the case while he is still involved with Kirsty."
Tyrone confided in Fiz regarding Kirsty's domestic abuse a few weeks ago, but he currently feels unable to leave his violent partner in case he loses access to their daughter Ruby.
Coronation Street airs Fiz's injury scenes in a fortnight's time.