Utterly fantastic!
Man, no one does clothes better, great job! There are a few minor issues with this though:
1) The skin tone around her chest is kinda inconsistant with the rest of her body.
2) Also there is something wonky with the lighting. The shadows in her cape are too dark given the lighting you are using (especially around her shoulder) and if the lighting in in front of her then she should be casting a shadow on the inside of her cape. I know I'm a nitpicker, sorry.
Again though great job. Good to see other poeple doing Powergirl manips.