Or, it could be just that she's bilingual.
I have bilingual friends who change back-and-forth between English and their mother tongue when they are emotional (excited, etc.) and they don't seem to give it conscious thought. Perhaps you're right but I just assumed that when she gets excited she just reverts back to her Italian... ...on the pure blue path she does this, too, but I didn't notice her dialogue being as hostile toward Doug as you're showing here. Perhaps another thing that is path-dependent?
The scene at the club I wrote about is the first time you're there, before you can choose between the Red and Blue routes. After the scene with Bruce and Stacy, Doug drives Raffa home—well, Doug drives while Raffa fingers her asshole.
Afterward, they have sex in her room and on the balcony, during which Raffa tells them what she did in the Club. After that you choose the route, if I remember correctly.
The fact that Raffa is already so hostile to Doug in the scene with Bruce and Stacy suggests that she doesn't actually love him.
As we learn later when Trevor appears, Raffa is from Italy.
But Doug doesn't even know which region of Italy she's from, which indicates that he doesn't know much about Raffa.
Presumably, the two got together quickly and married just as quickly.
I suspect that Raffa had to leave Italy for some reason.
She may have already been a Slut in Italy, and perhaps she had an affair with a man she shouldn't have.
This could have something to do with the Mafia, who may have then banned Raffa from Italy.
Raffa probably entered the country on a tourist visa, and to be able to stay, she needed a husband.
Raffa met Doug after her arrival, he had probably been single for a while.
Doug seemed good enough for Raffa at first, he had a job, appeared to be a nice guy, etc.
Doug was, or probably still is, so in love that he doesn't really notice any of this.
Raffa complains that Doug is manipulating her into being a slut, she accuses him of being responsible, when we choose the red path.
I suspect that Raffa couldn't stand the life of a good woman anymore and is presumably manipulating Doug to indulge her lust and desires, regardless of whether Doug wants it or not.
I suspect that Bruce is a descendant of Italian immigrants, his uncle is probably Italian, and Uncle Trevor likely has connections in Italy.
It's possible that Bruce/Trevor's relatives know what Raffa did in Italy back then, and Trevor probably knows why she emigrated and married Doug.
Who knows if and what Trevor will do with this information in the future?
He could blackmail Raffa with her past.
If she doesn't do what he says, Trevor could tell Doug everything about Raffa's past, which might give Doug a reason to divorce her.
Raffa would probably be deported to Italy, and who knows what fate awaited her there.
Trevor and Raffa also spoke briefly by the pool, but unfortunately, we don't know what they talked about. Shortly afterward, Trevor left.
What I've written here is speculation, but it fits the story quite well...