Yelena Belova.

It's funny... like you I bought a 2nd Black Widow to modifiy but my plans were to give her the gold (rather than silver) equipment and to (hopefully) make the hair look better.
Like this I guess:


However, I also considered trying to make her look like she did in the 90's, which was like this:

(It's a terrible pic but Ron Lim used to make it look good during his run on Captain America.)