Well I would assume this is Shana putting on a Nena wig, instead of Nena dressing as Shana. The breast size tells it all, Shana is way too much of a Pettanko compared to Nena.

Well she is asking what Cosplay it is and it says "Shana" in the bottom corner so this really should be Nena cosplaying as Shana.

That big bow is in the way so the breastsize is easily hidden.
And of course then there is the eyes. Shana has red eyes when transformed and a faded dark brown eyes when in normal form. Nena has yellow eyes. This picture has yellow eyes.

And if non of that convinces you, I am pretty sure I read on the artsist website that this is supposed to Be Nena cosplaying as Shana.

If you know the website this came from, put it in as the source and tag the post with the artist's name.