Very nice image but everything seems to not blend as well as it could. The horse looks very fake. I think matching the woman's hair with the horses tail also makes the image look rather funny.
A good attempt in creating this mythical creature. I like how you decided to have an action shot of the the centauress aiming her bow (the archer in me is trying not to wince in that the bow and arrow is not quite being held right). Your pasting the centaur into the scene is good; no haloing around the main subject. However, the centuar does not appear grounded; fully there in the scene. By that I mean she appears to be floating because there is no shadow cast on the ground (you do have shadows on the underside of the horse belly and under her arms but no shadow on the ground. Creating a shadow would fully ground her as being there on the trail. (not sure which program you are using so you may have to poke around to accomplish what I am suggesting) One way to do that is copy and paste your centaur into another layer set at Normal 100% over the original then lower the Brightness to -300. You now have a full black silhouette. Flip that such that it now mirrors the centaur. Apply a geometric effect that will skew or slant it to the left. Lastly, adjust the Normal setting on the layer from 100% down to 7-15% which will make it a faint grey transparent like a shadow. I think that the tail hair is a tad too sharp edge in some spots and is a little to close in resemblance to her head hair. Feathering to avoid hard edges a maybe some directional blur to give a windblown look might help to improve it. Lastly, the composition overall looks a tad washed out (at least on my monitor). It could do with a little boost in the contrast department with playing with the Shadows/Highlights/Midtones to get a greater tonal range throughout the image. Hope some of my suggestions help with future compositions.
I think this is a pretty good shot, i just think the creature would look less cut & paste on the background if you add some sort of shadows underneath.
Basic composition is fine, but it would benefit from the addition of a shadow underneath - without it the centauress seems detached from the ground she is standing on. Bonus brownie point for the correct archery position :-)
I really appreciate that you made this brave effort, instead of just taking a photo of a statue.
However, your Photoshop skills are ..... well..... very much beginner level.
Send me a message if you'd like a bit of help with it.