YES SHE IS!
JRulez I'm going to tell you the must see Mercy eps when I'm done with it. Some have no Mulgrew (this is why the show was cancelled, obviously), but others have fabulous Mulgrew.
Like this ep, Destiny, Meet my Daughter, Veronica
I am so impressed at how every single line that comes out of her mouth in this show is a classic. It's like she had some special writer and the rest of it was written by monkeys. What would really be great is to have all of her scenes in a youtube.