Beautiful villain. She has the feeling of being competent, manipulative and knowing very well how much she worth is. The cleanliness of your line art and colouring are top notch. It is simply pleasure to look at art like this.
Within the confines of the story, the destruction and suffering she leaves in her wake more than makes up for her unassuming appearance. Her clothes are also designed to be "different", as I wanted clothing from her realm to be unlike anything you would see a human wear. It's a combination of something regal and yet not to demonstrate her personality.
But that's the thing, the clothes aren't really that original or different, they look pretty generic/bland, especially the skirt/boot combo. Maybe some complex embroidery and more layers could help build that "regal yet not" level you want to achieve, but it's not there yet. Also, the dark hair in red villain has been done to death, try adding a splash of another color to spruce it up a bit (Even nude color lips would be a great improvement). No matter how many evil things a character does, the visual of their appearance is still what's gonna stay with the audience and grab their attention. It can't be too boring nor too complicated, just enough to give them some staying power. This is just my two cents and I don't wish to upset you, but right now she's pretty forgettable.
A simple design works just as well as anything layered or embroidered. There are tons of memorable villains that wear something incredibly simplistic; for example, Medusa from Soul Eater wears a black jumper with a hood and that's it, but she's remembered for her acts, not her outfit, and what's more is that she has three appearances. Hard to be remembered for your appearance when it changes that many times within a short time frame. There is a splash of other colors too: the aquamarine of her choker's gemstone and her eyes. This is also one of many outfits for this character, and red isn't her only color. The outfit I gave the artist as a reference is black and blue, for example.
Also, as you said, this is your opinion, so your saying that she's forgettable means very little, which isn't to say that your opinion is worthless or shouldn't count, just that yours is one opinion amongst many, many others. Personally speaking as her creator, I'm quite pleased with how she looks.