I was thinking she dresses like the woman in the picture.
So she's going to look like an overpriced planeswalker?
I find that, from your postings, you're not understanding how most forums work. When you have a question, you can post... But don't seem to make a demand and then pester. We provide criticism and assistance much more readily with honey than vinegar.
Also I heartily suggest 'throwing in' on things you may know about... If you aren't comfortable with the rules as of yet we have numerous threads open at any time discussing various topics. People are receptive to providing help when they know you're not just here for the brain trust.
Alright. So you're looking to stat a creature out. Well, first off... If it is going to be a PC speak to your DM with your expectations, what you want to do, and go from there. If it is a monster?
Well, the system exists. What you seem to want is a half-fiend with some specialized abilities and a look. The look is mechanically meaningless... A statblock can represent anything. All you need to do is take the classes you want, combine them with your base creature type, add any templates... and voila!
If you want to check out the system on advancing monsters the information is included in your edition's version of the Monster Manual, with nifty tricks. You may also want to look at various tools for 'quick advancement', but I am firmly of the school of learning the math before using a calculator. It helps you to see the inherent (il)logic of the system, and will make you a better player and DM.
Slainte,
-Loonook.