Well, Brainheart, I'd love to see a full blown fictional story - Ashley centered, with Shepley in the end *g*
Besides that - I don't know. Maybe a prologue with Ash and her 212 before Saren attacked. After that ... well, we all know ME1 and the story. Most interesting part here is to describe how Ashley slowly became more and more trustful towards Garrus, Tali, Wrex and Liara. And of course, the development of her love for Shepard.
ME2 can be interesting but also the lowest point of the entire story - beating the reader down, so to speak. Did Ash go after a new love? How did she deal with the loss of Shepard? And what did she do while not in touch with Skipper? Promotion to Operations Chief and LC?
ME3 ... well. We all know what we wanted - and what we never got.