De Martini auditioned for multiple roles in the new film, but was hired to help coach GaGa's co-star Salma Hayek, who was struggling to nail her accent.
And now she believes GaGa, who plays murderer Patrizia Reggiani in the movie, could have used a little extra help.
"I feel bad saying this, but her accent is not exactly an Italian accent, it sounds more Russian," she told The Daily Beast.
That won't thrill GaGa, who spent months trying to nail the accent for her portrayal of Reggiani, who hired a hitman to murder her ex-husband, Maurizio Gucci, in 1995.
"I lived as her (Reggiani) for a year and a half," the "Poker Face" singer told British Vogue, "and I spoke with an accent for nine months of that. I never broke. I stayed with her."
GaGa, however, is very happy with the way she sounds in the film, telling "Good Morning America", "I was just in Milan the other day doing a television show and when he (host) told me that he was so impressed with my Italian accent and Italian people were impressed with my accent, I couldn't think of a higher honor."
In a separate interview, the "Shallow" hitmaker told Sky News it will be hard for her to shake off her "Gucci" character. "I would say that in terms of letting the character go, I don't know that I'd ever let her go," she admitted. "It took me years to shed Ally from 'A Star Is Born', and I think the same will be true here."