I like the striking contrast here; you do a great job of showing us the twisting and warped flesh, the distortion of bone and teeth.
And I especially like the way the monstrous side is pulling away from the center, as we see in the outward arc of hair, brow, upper lip, and chin; if it were just divided exactly down the middle, it'd look more like a fixed and balanced condition (or a before-and-after ad) rather than a moment of warping horror.
I'm a little puzzled by why the monstrous side shrinks her eyeball and narrows its view with tighter lids (both of which would normally be protective mutations) but also pushes the eye forward so it is LESS protected by a bony socket than most animal & human eyes. But I'm not saying that contrast is a problem, as such, since it also makes it more unnatural.
My only serious crits concern the tattoo on our right and the ear/earring on our left.
The tattoo looks completely unrealistic to me; a flat color layer you added on top rather than a real mark on human skin. I do see the shadow and highlight you added, but they have that shallow vector look; nothing even hints at the texture or color differences of natural skin or the tiny soft highlights of skin hair.
Unless the axe tattoo has vital meaning here, as either a runespell that causes her transformation or the mark of a relevant cult membership, I'd strongly recommend removing it, since it both requires more work to be realistic and lowers the contrast between her apparently innocent and evil sides. But if it does have meaning and you keep it, I'd recommend making it smaller and less distracting--which will also make it easier to texture/shade as something real; the large size makes any problems more visiible.
And I've got two problems with the ear on our left: the piercing socket and the shape of the ear itself.
If you look at any healed piercing in human or animal flesh, you'll see the hole in the skin has rounded edges where the flesh pulled together in healing, rather than a flat-edged hole like notebook paper. A clean and healthy piercing just indents the flesh with a soft rounded inward curve that looks as natural as the earlobe's outer edge or the rim of the nostrils, and since we assume this ring is on the woman's own ear rather than magically appearing with the other monstrous aspects, I'd recommend going with that clean curve.
(If a piercing or the material of the ring creates a strong skin irritation, you can end up with something twisted, swollen, maybe with lumpy keloid scarring, but I recommend against that here; it would draw more of our attention to her ear rather than the warping-aside of the main transformation, and the distraction could weaken the primary impact--especially if the ring's effect was strong enough we wondered whether IT was responsible for the transformation, etc. So I'd go with smooth and natural as well.)
But--and I don't think this will surprise you--the current shape/lighting of the ear is odd enough to be a distraction of its own.
The inner lobe edge, ragged and a little torn, looks almost paper-thin, rather than having the thicker edge we'd expect from even a cat or rabbit. The shadow and lighting is confusing, making the brighter-colored streak just above the ring look like it's a thick forward curve, which makes that thin ragged bit look even odder (does any animal have a thin flap in FRONT of its entire ear-riim?) and the smoothness of color on both that bright-colored arc and the flat pale surface of the ear itself look brighter and smoother than a human ear, unlike the rest of the transformation.
As a result, it looks kinda like, I don't know, a white-chocolate-coated sugar cookie with the bottom pushed out and upward from the normal human position.... Not exactly monstrous, and its bright contrast to the darker hair and flesh makes it even more eye-catching.
Me, I'd like to see both a more meaningful/monstrous ear shape AND one that doesn't draw our eye so much away from that outward-warping transformation.
Animal ears wouldn't push the bottom lobe away from the head like that; they'd flare the upper/outer edge into a higher/wider fan to catch every sound, as most animals have. Whether the earflap pulls back almost flat to protect the edge from whatever this creature is attacking, or the top folds down and inward (cf pit bulls and boars) to protect the earhole, it'd still be fairly flat to the head.
Or, if the smaller and more lidded eye means that this monstrous head is designed to show few weak points, the ear might be mostly a small hole protected only by a a gnarled ridge of slightly raised flesh, which would be even less visible behind the hair.