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Posing is your next big area for improvement. In 3 and 4, she looks larger than she needs to. In both instances, her butt is closer to the camera than is her head. A good general rule to help posing is whatever is closest to the lens looks largest. This is why you usually want a girl's weight on her back leg (farthest from the camera), which in turn means you usually don't want her square to the camera, but at an angle.
If you have her put her weight on her back foot, then the front leg will usually bend at the knee, which will also tend to help create a nice "S" curve, a good feminine look.
Re: the watermark, ask yourself what the point of a watermark is. Why include it? Mainly, it's to provide breadcrumbs to viewers who don't know you so they can find you. Your name, or your company name, are very useful. A design element is a lot less important, unless it is very widely known.