I think Danni is almost certainly ND and her 'alrightydoody' cheery stream of patter is her way of dealing with the world.
In fairness, if I had a temporary personality transplant and applied for GBBO, I would be weeded out within five seconds of the bit of the casting they do while being filmed baking, because I'd be snarling 'Get that camera off me and stop asking me questions when I've just curdled my creme pat or dropped my tuiles!' so I genuinely admire anyone who can bake competently and deal with the judges and presenters interrupting them and narrate what they're doing adequately for the camera.
(I suspect it's why there has always been a strand of medics who did very well, despite being very time-poor, because they are used to working under pressure while being observed and have dealt with endless assessments on the way to qualifying.)
I always remember what that ICU consultant baker in season 3, Danny Bruden, said on her blog about being in GBBO. That everyone involved in the show is very nice, funny, charming, and professional, crew and presenters alike, but ultimately, they're making a product, and you're not that product. You are just the ingredients, taken out and used for filming, and then put away again.