Are her breasts supposed to be bound, in lieu of her wearing a sports bra? If so, they're really, really round for that; compression-style jiggle controlling bras/bindings flatten the breasts and spread them out quite a bit more than that. Usually the cleavage won't be of the straight-line, sort - more of a soft hills kind of cleavage if anything. Very few well-fitting bras will give the sort of cleavage you've got going on here. They should feel more uplifted and supported, as well - right now, it looks like her binding is *really, really loose* because of how low the breasts are sitting. Those things will flop all over and *hurt* when you're trying to be athletic. A compression-based sports bra/binding will push a lot of the breast tissue up and nearer the body, giving it way less projection.
See this lady in a shock absorber sports bra (one of the better quality compression-based sports bras available):

Only an encapsulation-based sports bra would retain a round or pointy shape, like this one from Freya:

And in an encapsulation-based bra, the breasts are separated and lifted, not pushed together to create line cleavage.
Admittedly, you may choose to go for a less realistic breast shape and design as an aesthetic choice, but I'm a big proponent of realistic and well-fitting boob-clothing in media
