about the costume:
i'm kind of a rookie in this stuff. i could give her a better costume if it was hand drawn (in paper or tablet). so, i call this costume SLOTH XD
i understand your point, anyways. i'll make a completely new witch from scratch, including new costume, when the semester in my college is over. because if i keep changing this one, i'll never finish it, u know?
about shading/anatomy/that kind of stuff:
as i said, i'm a noob 
i have a lot to learn yet, patience with me 
Maybe you shouldn't blame a bad costume on which medium you started from, because either way it started from your imagination. Decide which direction you're going in first to make sure the elements are unified--say, maybe you want it to have some African elements or, I don't know, maybe make it look closer to Chun Li's costume. Then, I suppose, you could look up some pictures to get more inspiration from and copy-pasta them into an assorted
bowl of clippings. (Ignore that, that was a pun.) And of course, practice. ...I'm not picking up the
ConceptArt virus am I?
IMO, the anatomy's good enough--it's just the shading and palette choices you need to work on, I think. Regardless of whether or not you're going to make a new witch, these are things you need to keep in mind to improve.
