If this makes you feel better: I've seen horses drawn A LOT worse than yours. ^^ I mean it looks a bit original but not particularly wrong, if thats what you think. It might help to make the hooves bigger instead of these deer-like high heels. Ovrall I really like the colors and the girl looks interesting as well...too bad she drowns people.
The difference between the two it that while both have the base figure of a horse, the Hippocamps/Hippocampus can be depicted with scales and sometimes fins replacing the hindquarters. In Greek mythology they are said to be created my Poseidon and pull his chariot. Kelpies are usually described as having black skin the texture of a seal's with the ability to transform. The exact transformation differs on where you're getting your information from. Some will tell you that they transform into a beautiful woman who is dripping wet(sometimes with reeds or seaweed entwined). Another that I've read says that they keep their horse form which is perfect and elegant with a mane that never dries, but that when they are in the water, their hindquarters can turn into water allowing for ease of swimming. In both tales, I've read that the nostrils excrete a mist or pheromone that lures humans close, especially children. The human transformation will grab them once they are close enough and pull them to the bottom of the lake/river they inhabit to feed upon them. The horse form pretends to be docile, allowing someone to ride them and then carry them off to their lake/river to devour them.
If you say you "suck at drawing horses", why not practice 'till spasm? Try with a real life reference photo? Or maybe try tracing a photo without posting the result anywhere. Keep it like a reminder that you need to draw horses better. Or if you're not really interested in drawing horses, don't give any fucks.
So cute! I like the braid that stays a braid regardless of her form, and also the way the ponytail in her hair mirrors her mane and tail. It's a really cute design and her outfit and watery fish and flora look both natural and fantastical- like she's not human, but could pass as human when necessary.
(Also, this is going to sound kinda racist, but when I saw "black girl in green" I immediately assumed "daughter of Tiana and Naveen from Princess and the Frog", then her name being Charlotte I thought they'd named her after her friend etc etc...)
WHY IS SHE SO ADORABLE!? I've never seen a kelpie original character before, and I'm a mythology freak, but if I did Charlotte would definitely be one of the more high-end ones! This is really great, her color palette just... great. Dark brown and green just looks fantastic. Love her skin tone.