You said she wasn't a succubus, but there is other kind of demon out there. She could be half succubus, half demon of something else. Hence the reason why she isn't one, but have some ascendance of it. Maybe she had parents of different ethnic. Eh! We have that here on earth, why shouldn't it also be like that in Hell with all the kind of different demon in there!
But like i said, the wings could be there or not, like she can hide it or not when she wants. Some demon only pop them when they are needed (to not harm them, and since it's not always easy to move with them) or to just show off and make an imposing presence. Demons ranks and position of powers are important in a demoniac world.
Damn you drew the dress smaller too! But aside from the fact that if she were standing her dress would not reach her hips, she looks really cute. She's got the wide eyes and pouty lips I missed from the Lowroad characters. Very adorable. Is she a devil or any specific kind of demon?