Rigg will appear with her daughter Rachael Stirling in the Mark Gatiss-penned 'The Crimson Horror', which will centre on a mother and daughter harbouring a dark secret.
Speaking to Vulture, Coleman offered the first hints on what fans can expect from Rigg's guest appearance.
"Oh my God, she was so funny on set. She's got a lot of banter on her," Coleman declared. "I think [co-star Matt Smith] described her role as an old hag - but in the best possible way."
Coleman added of 'The Crimson Horror's storyline: "She's our villain and she runs a place in 1800 Yorkshire called Sweetville, which is kind of Stepford Wives-y. She has a big factory and she's up to no good.
"Her daughter, Rachael Stirling, is also playing her daughter on the show, and they just go at each other."
Coleman also spoke more generally about the secretive nature of Doctor Who showrunner Steven Moffat's plans for each series.
"He's good with his secrets. But I was quite adamant about not needing to know," she said. "Matt didn't know [Clara's mystery] either, not until the script came through and then we were both like, 'Aaah!' It's also always a work in progress."
She continued: "We go through a lot of script changes, things are always evolving and being tailored, so I think Steven likes to play things close to the vest until he's sussed them out properly."
Coleman will additionally be starring in the upcoming Doctor Who 50th anniversary special, opposite Smith, former Doctor David Tennant, Billie Piper, Joanna Page and John Hurt.
The BBC revealed earlier in the week that the 50th anniversary special will also see the return of the classic series villains the Zygons.
Doctor Who airs on BBC One in the UK and BBC America in the US.
Watch Jenna-Louise Coleman discuss the upcoming episodes of Doctor Who below: