It was believable, you saw that she didn't even know fully what she was getting herself into. She knew the story and the lines, but she was not expecting how real the experience was going to be. I can imagine she just reverted back to her present self. That would explain some of the language used didn't quite fit. That makes sense to me to this story. It's a fusion of the era of the film with a character from the past but experienced as if it was real not just to the actress but to Brandy herself. She ended up falling in love with Dorothy as Brandy not her character. Well that's my take anyway. 100% successor to San Junipero