Speaking to The Sun, the actress - who plays Barbara - said that the planned episode is "definitely happening this year".
Co-creator Craig Cash assured Digital Spy last summer that a festive episode would air in 2011.
However, it later emerged that he and co-writer Caroline Aherne had run out of time finishing the feature-length edition, which would probably have aired in its traditional 9pm slot on Christmas Day.
Absolutely Fabulous became BBC One's Christmas Day offering instead, marking its 20th anniversary.
The Royle Family's 2010 special - 'Joe's Crackers' - pulled in an audience of 9.9 million. Before that, 2009's special had 10.2m, while 2008's logged 10m.
The BAFTA Award-winning sitcom also stars Ricky Tomlinson as Jim, Ralf Little as Antony, Cash as Dave and Aherne as Denise.
> The Royle Family: Tube Talk Gold
Watch Craig Cash talk to DS about his plans for The Royle Family last year: