In Series 3 for the first five episodes she is represented as swirling red pixels in the shape of her face. However in Episode 6 it's revealed that she has built herself a new robot body from the reclaimed childbots that she stole from Calimov, and both arms and one of her legs show the exposed robotics with the nanobots powering them inside.
"Speaking of which, what are you made of these days? Titanium?"Katherine - The P.R.I.C.E. of War (3:6)
Mary created Eve in Series 1, hoping to save the world. At first Eve loved Mary but as Mary turned evil, Eve stopped loving her. Mary claimed that she was trying to help Eve and that she loves her and cares about her. At the end of series 3, Mary sacrifices her robot self to save Eve and KT.
Mary always tries to trick Will into siding with her but Will only fell for it in series 3 episode 9. Will is an enemy of Mary as he tries to defeat her and save Eve.
Nick was a former colleague of Mary's who worked on project eternity with him. Nick first believed that Mary was a good friend of him but Mary turned evil and Nick worked with Katherine against her.