I found a photo of her on Twitter, where she says she’s wearing a 65L (Eu) size, which converts to a UK 30HH.
While she sometimes looks as though she might be in that category of size (depending on the photo), I’m pretty sure she’s bigger than a 30HH, as she has much more volume in her boobs than most 30HH women I know.
Perhaps it’s somewhere in-between and her height and build are deceptive. I found other photos of her wearing bras, but they’re from over ten years ago - she’s changed significantly in that time.
Add: the other thing I've noticed about this photo is that the centre gore looks reasonably snug (it could be better), which means she's wearing close to the correct band - but her boobs are spilling over the top of the cups, which means she needs to go at least one cup size up, possibly two. In the rest of the photos in the set, her back band seems to be behaving, but the shoulder straps look like they're hurting her - which tells me (again) that she needs a slightly bigger cup size.