She told the Radio Times that she had been supported by her co-stars Matt Smith and Michael Gambon.
"I've not done any acting before, so I wasn't sure if I even could," she revealed. "But I read for the part and on my 30th birthday, they called to say I'd got it. Matt Smith and Michael Gambon have been really encouraging. I can't wait to see the results."
Jenkins added that she had observed Gambon's acting technique throughout filming.
She said: "I learned so much from simply watching Michael Gambon, and he was always telling great stories about all the actors he's worked with. Matt and I would sit and listen to him for hours."
Last month, the singer praised the Who cast and crew on Twitter after completing work on the episode.
The Doctor Who Christmas special will air on BBC One in December.