Harman's character Sasha Bezmel has faced a turbulent few months in Summer Bay, which began when her boyfriend Stu Henderson (Brenton Thwaites) started attacking her.
More recently, Sasha has confessed that she was responsible for Stu's mysterious death, which is being treated as a murder by the local police.
Mammone, who plays Sasha's father Sid Walker, told Digital Spy: "Demi is a lovely girl and a talented actress - she has handled this storyline like a veteran."
This week's episodes on Channel 5 in the UK see the Walker family rally round Sasha following her confession.
"While shocked, Sid quickly moves on to support Sasha, as he totally believes that it was an accident," Mammone explained.
"He actually feels sad and disappointed in himself that Sasha didn't feel safe enough or trust that Sid would support her if she told him the truth from the start of the problems."
Asked where things are heading for Sid in the longer-term, Mammone replied: "Let's just say that things don't get any easier for him."
Home and Away airs weekdays at 1.15pm and 6pm on Channel 5 in the UK and weekdays at 7pm on Network Seven in Australia.
> Read our full interview with Home and Away star Robert Mammone
> Read more Home and Away spoilers and news