You are right! That's what they call a crown and the space was intended, I think it adds to the clean appearance of the image.
Thank you for your suggestion anyway, it is appreciated.
This is a good photo. You have excellent DOF and it is nice and sharp around her eyes!
So well done for that.
If you don't mind me saying, it could be even better if it wasn't so much in the centre and composed with the rule of thirds in mind.
I would have eliminated the space on the right and give it a little more room on top as well as to the left of them, to open up where she is looking (basically position her eyes on the meeting point of the top horizontal ant the right vertical line)
Have a look at this link, so you know what I mean. http://digital-photography-school.com/rule-of-thirds/
This would add much more impact to the image and make it a great shot.
Hope you don't mind, this is just my opinion.
Thanks for sharing