I like the design, but like someone else said she does look kind of old. Just some constructive criticism here, don't take it like I'm being a jerk, just trying to help, but I think maybe if you got rid of the lines around her chin and on the cheeks that might help make her look younger. I have a problem with this sometimes too, but if you try to draw in eyelashes sometimes it ends up looking like wrinkles around the eyes too. Other than that I'd say just work on proportions a little more. I think you can make her shoulders a little wider to make them fit better with the size of her head, just not too wide to make her look like a dude with a dress on.
If you make the shoulders wider, leave the ribs about the same. Maybe a little narrower at the bottom even. Right now she looks a little anorexic since her ribs stick out farther than her breasts, and I mean we are talking about Wonder Woman here, she's got curves on her, so if you even that out and give her some hips you're good. Keep workin' on it, it's hard drawing women, you'll get there.
hopefully I get the hang of female characthers soon, glad to see you guys like the costume, even if my WW looks odd, old, sick and extreme size zero in apperance lol

