The old Character Sheets had Mimi being able to communicate telepathically, instead of vocally. She preferred this method over vocal usage because she could send the "perfect" message in that not only do you understand her completely, but there was also a emotional level behind it.
Grids, the previous editor/writer for GT, made the statement that Mimi won't be talking because of damage to the vocal cords and other injuries she had sustained.
Will she speak? I hope not. I like her as the silent badass.
“Salvation comes with a cost. Judge us not by our methods, but by what we seek to accomplish.”
"To punish and enslave..."