Get it in writing somehow that you were fired BECAUSE of your stutter. You MAY have been fired illegally. Just ask in an email why exactly you were fired. If she mentions your stutter as being a reason, without anything else really being a primary reason, that may be grounds for a lawsuit. As long as you can effectively do your job despite your stutter, they can't legally fire you BECAUSE it takes you a little longer to say things (at will employment will hinder that quite a bit though).