A pretty good effort. A couple of thoughts on making it blend better:
1) Feather the edge of the woman before cutting her out of the original picture. This will soften the edge and make it blend more.
2) Brightness, the lighting on the woman seems to be even across the image. The light in the toad stool appears to be more from the right of the shot. You could apply a layer mask to gradient or adjust the lighting to her right side.
3) On a related note to 2, she is too bright for the location. lowering her brightness would make her fit better.
Great idea though.