|Billie says her stage debut is nerve-racking|
Billie's character, Ann, replaces her egotistical boyfriend Dave (Kris Marshall) with the more 'conventional' Patrick (Laurence Fox), only to find that she can't make up her mind as to what (or whom) she really wants.
Billie told the BBC's Richard Lewis that she has been nervous about making her stage debut in Treats.
"My knees knock every night. In fact, I'm going to go for some replacement ones after the show. It's absolutely terrifying.
"It's a scary job and I have the utmost respect for every stage actor I've ever watched."
Billie starred in an adaptation of Philip Pullman's The Ruby in the Smoke for the BBC, screened during Christmas 2006.
|Billie's final scene as Rose Tyler, or is it?|
Earlier last year, we had said goodbye to her character at the end of the second series of Doctor Who.
"I miss not doing Doctor Who and I miss Rose Tyler. I hope I made the right choice.
"It's going to be really hard when the new series [with Freema Agyeman as Martha Jones] starts - I'm going to find that quite hard to watch.
"I had a great two-year run and I'm really enjoying myself trying other things.
"And there's always the chance that Rose may return. You never know - that's the beauty of sci-fi!"
Before travelling with the extraterrestrial explorer, she played Hero in the BBC's modern retelling of Shakespeare's Much Ado About Nothing.
|Billie in The Ruby in the Smoke|
She recently published her autobiography, copies of which she signed in her home town in October 2006 - click on the link on the right to listen to bbc.co.uk/wiltshire's interview in Swindon.
Billie is soon to appear in ITV's major new production of Jane Austen's Mansfield Park.
Treats is at the Theatre Royal Bath until Saturday, 10 February, 2007
It is then showing at the Richmond Theatre between 12 and 17 February and has its West End run at London's Garrick Theatre from 20 February 2007.