Her comments came as a film executive claimed that the film is in the works and production would likely begin early next year.
Froggatt, who won a Golden Globe for her portrayal of maid Anna Smith, spoke to the Press Association in Los Angeles on Wednesday at the premiere of her latest film, A Crooked Somebody.
She said: “Nothing’s managed to come together yet. It would be lovely if it did. But I think we are all kind of hoping something will happen.
“It’s difficult because we are all out of contract so everyone is doing different things at different times in different places.
“It’s kind of tough getting 24 main characters together at the same time.
“We are all keen to replay our little roles for 10 weeks and have a little get together and selfishly have a great time and hang out again.”
Michael Edelstein, president at NBCUniversal International Studios which distributes Downton, told the Associated Press on Wednesday that a film has been “in the works for some time”.
“We are working on getting the script right and then we’ve got to figure out how to get the (cast) together,” he added.
“Because as you know, people go on and do other things. But we’re hopeful to make a movie sometime next year.”
The ITV period drama’s creator, Julian Fellowes, also said this month that a film was “pretty likely”.
Froggatt, 36, stars in A Crooked Somebody alongside Mad Men’s Rich Sommer, who came up with the story about an attention-seeking, fraudulent psychic.