Holy fuck 
I spotted this girl some time ago on the Curvy Kate instagram page. Isn't she just beautiful?
In terms of size - in this photo (attached) she's wearing a Curvy Kate Luxe in biscotti - and this photo was posted in December 2019, so I'm assuming her size hasn't changed much since then. This bra goes up to an L cup in some band sizes, and from the photos, she's *just about* fitting into the cups, but the centre gore isn't sitting snug - so, it's possible she needs to go up one cup size (although, with strapless bras, it's often better to remain a cup size down, as it tends to hold you in better). I have one of these bras in black, and they are engineered to perfection - usually with strapless bras, you are constantly pulling the cups up and often fall out of them or sag badly - but these hold you in really well (the back band does all the hard work). I've also seen her model a Curvy Kate Hot Spot (which also goes up to K) and a CK Victory (also up to K), and she said it was a 30K she was wearing in the Victory - it looks a good fit, although, I can't see her back band, so can't be 100% certain.
Given her height and frame, I'd suspect she's in the 30K, 30KK or 30L category. Possibly 32K, as she looks broad.
It must be *very* difficult for her to find bras (other than CK) that fit - and even worse for swimwear.
But what a gorgeous girl.