Amanda admits that last summer was "brutal", as she juggled filming for both shows at separate locations in Cardiff and London.
Times have been hard for her Mr Selfridge character too though, having been left thoroughly heartbroken over her rejection at the hands of long-term love Mr Grove.
And she still has to face working with him!
"She's the consummate professional, so she gets her head down," Amanda says.
"Luckily Doris isn't there anymore, because that would have been too painful, I think."
But there is set to be plenty ahead to distract Miss Mardle, including a change of fortune.
"She gets left a house and a disposable income, which makes her more confident. Which means she turns a few heads ..." Amanda reveals.
Speaking of turning heads, Amanda had more than a few Sherlock fans in a spin when it was finally revealed that her role as laidback wife to sleuthing sidekick John Watson was all an elaborate ruse.
Yes, Mary Watson turned out to be a deadly assassin.
While the latest series ended with yet another cliffhanger, with Sherlock's nemesis Moriarty appearing to have returned from the grave, will Mary be back by John's side when the show returns?
Amanda says that's definitely a yes.
"Mark (Gatiss) and Steven (Moffat) are writing stuff as we speak and it's just a question of getting everyone together, hopefully this year," she adds.
"We know roughly what's going to happen, so it's fantastic."
It also means another opportunity to work with her real life partner Martin Freeman, who plays Dr Watson and with whom she has two children - something she says is a real pleasure.
"You are our benchmark," she jokes with This Morning husband-and-wife team Eamonn and Ruth.
Mr Selfridge returns to UTV on Sunday at 9pm.