Is it...?

I tell you this my dear. Like Kristy said, you gotta decide where you want the light to come from, then shade the other side. Also, the parts that are closer to us supposed to appear lighter, and the father darker. But you probably know that. You should shade her bum and the sides of the legs, body etc. I suggest you also take an eraser and lighten her face a bit, especially the nose. I think her butt should be further right for better balance. But still you've done a very good job for your first realism sketch. But wait a sec, wasn't your bro's pic realism?
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"No more darker than the night, no more mystery in sight. One day he was simply gone and who knows if he'll return."

Wow sweetie. For a first try at realism, you did quite well. As far as shading goes, I think you are off to a great start. Just remember that there is going to be highlight on the skin from a light source and it will only be coming from one angle. So if you have the light hitting the left side of her body, make sure you shade it to where the light will always be on the left side.Know what I mean jellybean? Just remember to keep it soft and when you blend, ahem (this is a piece of information given to me by MY muse MiniMaid) make sure you blend with a piece of tissue or something like that so you don't leave skin oils on your drawing. Otherwise when you go to erase, it will leave weird blotchy marks that will never come off and are quite noticable. For the hair, you can do it a bit darker and then to add highlights, gently take the edge of your eraser and lightly "brush" it on the hair until it "erases" highlights into the hair. It may smudge at first, but keep erasing and the smudges will erase. If you need any more help, feel free to ask me. All my love. mwah!