She is in Glasgow rehearsing with Keith Fleming for the Dominic Hill-directed Miss Julie at
the Citizens Theatre, an adaptation of August Strindberg's thrilling tale of an upstairs-downstairs liaison relocated to 1920s Scotland.
Television audiences will know her better as Molly, the lab assistant who only has eyes for Benedict Cumberbatch's character - and kissed him too - in ratings-winning Sherlock.
"It's been funny on Twitter because I get tweeted constantly by people saying I am the luckiest woman in the world because I've got to snog Benedict and slap his face," she giggles.
"It's been mad and the kiss in episode one of Sherlock was crackers. I have to say I got my chewing gum out for Sherlock."
She won't comment further on the kissing but she does admit she's enjoying working with Keith on the production which opens on February 6.
"The play was written in the 1890s and came out in 1906 - it was incredibly shocking and completely revolutionary. Strindberg did away with the interval and all the props were real, which had never happened before. It is still shocking now in its original form but there is something about bringing it into the 20th century that seems to make it more resonant. It feels a bit more like our world."
This is Louise's first appearance at the Citizens but she has worked in Scotland before, at the Tron in Glasgow and the Traverse in Edinburgh.
She is enjoying the particular challenges that Miss Julie's character presents.
"The received wisdom is that she's unlikeable. She's mercurial, imperious and coquettish but I think she's more innocent.
"One of the things about Strindberg is he wrote about the idea of character not being fixed, that you can't describe people as types; he was bucking against personality types. He was of the opinion we change constantly so she's hard to pin down."
Louise - who is staying with an old university friend and his wife in the West End of Glasgow while she works at the Citizens and is looking forward to a day off to explore the city - can now pick and choose the work she does.
But still tries to find time to write and says acting isn't far removed from her previous career as a journalist.
"I was interviewing actors and directors such as Ken Loache and Sofia Coppola and Shane Meadows and all these amazing people I really admired. I just didn't have the confidence at that point to try acting," she reveals.
"At a certain point I realised if I didn't try it, it might be something I would regret.
"So I went and trained in New York (at the Lee Strasberg Theatre, where Robert de Niro, Dustin Hoffman and Al Pacino among others started) and then with a French guy called Philippe Gaulier and then I did a little bit of fringe and got very lucky very quickly."
She got a job at the Royal Court Theatre without an agent, then found an agent and landed the part of nurse Roxy Bird in BBC TV's Casualty.
"There are plenty of people who are brilliant and don't get a break so you can't take anything for granted."
She says she is delighted at the success of Sherlock and the appeal of Molly, who was originally planned to appear in just the first episode.
"I think Molly is so popular because people relate to her."
She laughs: "It's obviously largely because she's in love with him and I guess there is the odd woman out there who quite fancies him."
l Miss Julie runs at the Citizens Theatre, Glasgow, from February 6-15.