Hello morozov-define,
Wow! you've done a ton of work. Let me see if I can help. You've had a very challenging critique request so I'm not surprised anyone has tackled it.
Question: I'm a little confused by this statement. She is an enchantress, and she is obsessed or possessed by a raven ?
If she is obsessed then everything is a style choice of her own making and she just loves those gosh darn ravens. If she is an enchantress that is possessed by an evil spirit then your drawings make a lot more sense to me.
I think both are there. I also don't think you are scattered. I think you are pretty spot on in most cases considering your thumbnail 'before after' work page. In regards to your guidline image which you provided a link for. I honestly find it lest interesting than your ideas. Your idea seems more fantastic and I think Igor Krstic's design is a bit more real world in its design elements.
His art seems to have good 'dark mood' and lighting and texture but his designs are a little...lets say, "less fantastic." than yours and more real world plain. If you look at his whole portfolio page you'll see what I mean.
In regards to your character you have very good shape language. It is repeated throughoutand offers the viewer an easy way to tell what it is.
However, your characters mask also seems very similar to the ones from Stargate. It looks egyptian is what I mean. In regards to its shape looking more hard surface than organic.
Lets take things backwards a bit and correct pure shape language with your thumbnail to explain some things.
The very first professor I had said that the most important things are, Unity, Hierarchy, and Variety. And I've come back to that lesson more times than I can count.
Lets push your thumbnail a bit. If your character summons ravens lets put a raven in there! We want to let the viewer know that's what she does. Lets communicate it. Also lets push the things that you wanted to emphasize!
For example: The slouched torso, the heavy dress, the branches, the helmet, and the feather shapes. When we exaggerate and push those ideas as shapes its easier for the viewer to understand quickly. And simple for us the artist to make design choices based on shape.
(right click, open image in new tab to read easier)
Also remember that you have an opportunity to make primary secondary and tertiary importance here in your design.
Other sugguestions could be:
:: Her possessed side hand is a raven's foot or claw.
:: Raven's feathers are more of a bra
:: She has raven's as actual shoulder pauldrons (because she summons them)
:: I prefer the thumbnails with the human face. The mask seems a bit much and stands out making it seem less of a transformation
:: Dont forget that her left shoulder (our right) needs to be there Here's an anatomical draw over for example
I think you've got a great piece here potentially so don't give up. I know its been a few months since you made this post and I'm late to the game. A bit more time and you are almost finished.
Hope that helped! Good luck and hope we see you again!