The red tint in the pupil only happens when you flash directly into the eyes and it doesn't get fixed in post. In other words, paint the pupils black, not a kinda grey-pink. I think that'll make them sparkle a lot more and look more natural.
Another thing I'd recommend is darkening the outside ring of the iris. You can't tell from the photo, but for most people the iris gets darker towards the outside, if not a quite well-defined outline/ring.
About the diamond sparkles: Currently they're a bit far away from the diamond and look like... not diamond sparkles. Try 1) moving them closer and perhaps toning them down a bit, and 2) add a bit of glow from the diamond (as I think I can see in the picture).