Hi Gemma,
Yes – so warm-up-wise, I find that long, open-throated vowel sounds help! So “yar yar yar” scales perhaps (in a posh English voice!) and focusing on each vowel with a more dropped jaw and open throat (ask her to make each sound with a slight yawn). I also find that arpeggios over “Bella Senora” is great for that. Just singing it as “poshly” as possible!
Song-wise, perhaps listening to a bit of London Grammar? If you can get the student to mimic this sound as she clearly mimics easily if she’s picked up the American accent. Tom Jones is another good example of a singer with that rich, open-throated sound!
Hope that helps:) good luck!