Firstly, lets address the picture.
As usual, the design is exquisite. I appreciate that you want to branch out into other fields, but you have a true talent for ponies. I very much admire the romantic style, as opposed the canon, cartoony style. And what always gets me, is the musculature that you detail. It looks like a real horse (pony).
As with the body, the wings are fantastically done, and I find the detail in the feathers' shading on-f***king-point.
Queen Isa is a true black beauty, elegant and toned, wide-winged. the small detail of her ears is well done, as is the ornate length of her horn.
Her cutie mark is a fascinating choice, the shaded red serpent is a stark contrast to the typical kinds we see.
Her breast-piece is of the familiar style to the other princesses, but it's her helm that stands out. Unique to her, and positively imposing, I think it's fantastic.
The flow of her mane/tail is an interesting choice, reminding me of several European flags. It makes me think that it might be an example of the Shadonian royal standard.
Oh, and I almost forgot, her boots. Elegant yet threatening, they look like they were crafted to be worn by royalty, and slash a throat if need be. I understand that she abhors violence, but she looks every bit the art of a warrior queen.
regarding her personality, she seems like a complicated pony. At times, just as beneficent as Celestia, and other times as willful and dangerous as the worst Roman Emperor. The nuances of her character are reasonable given her traumatic foalhood, (is that a word?) and unique life as one of the most powerful creatures in the land.
I like to think that every OC is derived from their creators own personality, at least some distilled quality. So I wonder just how much of You I'm reading about in her profile.
The backstory listed here is an extension of your already fantastic work, which I reviewed previously, and adds a lot of dynamic to the myth.
Where I had to deduct points: It's an inspired fan-creation, so I can't give 100% originality, but I can go pretty damn close.
Your technique is far better than anything I cold ever draw, as in my own medium, I'm always finding areas of improvement. So I don't think you'd ever want to settle for where you're at, like any artist.
I still don't think that 'Impact' is something that can apply to every work, but your style of drawing ponies has inspired the aesthetic my own character, so I have to give high marks nonetheless.