The actress - who plays the mother of lead character Will McKenzie (Simon Bird) - admitted that another full run of the E4 comedy is unlikely, but confirmed that she would return for any TV specials or a sequel to this summer's movie.
"I'm sure I would do it - I've had such a great time working on this I wouldn't be able to resist," she told The Mirror. "But I very much doubt there will be another series.
"Perhaps in the future a Christmas special, or some other one-offs might work, but because of where the story has taken the four guys I don't think it could sustain a series again."
The 40-year-old added although she is grateful to have received her "big break" in The Inbetweeners, she fears that the role may come to "define" her as an actress.
"[The Inbetweeners] has really exploded in the past 18 months - but that's the nature of being an actor, you work for years and then suddenly get your big break as they call it," she said.
"You strive for that for years and suddenly that role defines you for a while. It has been a great year, but I do hope that at some stage in the future I might be seen as something else as well."
Stewart-Wilson told Digital Spy in February that stars Bird, Joe Thomas, James Buckley and Blake Harrison have become "too old" for another series.
The Inbetweeners writer Damon Beesley said in June that the movie represents the "final piece of the jigsaw".
> 'The Inbetweeners' writer Iain Morris, actor Blake Harrison deny sequel reports
Watch Digital Spy talk to the Inbetweeners cast below: