If I recall correctly her mother said something about it in an interview about a play she wrote that was about to premier in a theatre. Because this play has to do with the relationship between mothers and daughters as well, the interviewer naturally couldn't help but ask about Keira. I think Sharman said she'd tried to quit smoking, so now she stole sigarettes from Keira's apartment at times. Something like that.
Is it true? Not a clue.