She is Mar-Bell from some alien race that came to Earth and became a hero. She has the ability to turn her entire body into marble! Of course while she is in marble form she cannot see, hear, taste, smell, or move. She can essentially just strike a pose and hope for the best.
Yes, another OC from Matt.
Drawn in Clip Studio Paint Pro on a Surface Pro 4. Here is the timelapse video:
And here is the B&W line art version: