Her knowing about it is good so she won't be caught off guard. A great thing to do on any date is ask her a lot of questions about herself, and this also means you can give yourself some time to warm up and calm down. Plus you get to learn about her and decide if you could be a good match. If she is a good match for you, she won't mind the stutter. Remember that non-stutterers might be slightly uncomfortable at first but they don't have anything like the level of negativity about stuttering that we can have. Good luck!