Would she possibly be more comfortable with a moulded sports bra in that case? A lot of teens are exceptionally paranoid about their nipples at the best of times, and the dominant teen bra styles do tend to be moulded. I suspect part of the problem is that a huge number of her friends will be wearing ill fitting 34a from H&M/New Look etc when they're really a 28D, and because she's wearing bras which fit properly those styles are out of reach for her.
Doesn't solve the sports bra issue, but Cleo has a few moulded bras (and some new ones coming out this season too) which she might find acceptable style wise for day to day wear but which are the sort of brands she probably needs to get used to wearing - just because chances are if she's a DD now she's going to grow a fair bit more. There's the Neve, Koko Icon/Flirty/Mode and Maddie
For the sports bra, what about this Freya one? The shape is closer to some of the VS pink ones. I think the VS ones all look less bra like and more crop top style so that might be part of the issue. The Shock absorber, you can see where the extra boob support is at the front
The Panache sports bra is also moulded, and looks very crop top-ish on.
Those are probably the ones which are good supportive bras, but look the least like "big boob" bras IYSWIM
One other wild card which might be worth showing her is this from Shock absorber. It only goes to a DD so it probably isn't as sturdy as the ones which go to an H cup, but a lot of the VS ones had the zip front, v neck design
If you can, try to keep her away from VS, they're bloody useless...you know they measure for bras by measuring under your armpits