Quick question!

Quick question! Hi, forewarning, Im really sorry if I phrase this poorly and possibly offend people, but just know that I truly do not mean to upset anyone! I work at a food place and we have a regular who has a stutter, however I have never knew the best way to speak to her. When she wants to order something, I usually know what she is trying to say, however I always feel like I’m being rude, or look impatient if I say it before she has finished, however I also feel like it may she would appreciate me saying it before? I don’t know if this make sense, but I hope someone can give some advice, because I genuinely just want to be nice and helpful to her! Thank you