My LAQ when I drop off a quilt to be done has them in the order that they arrive to her. If you need a quilt done by a specific date then you need to make the appointment in advance even if the quilt is not done. If you don't have it ready for her when the date arrives then you get moved ahead. I also was have to keep in mind that she is is 5 months out on her appointments. She has never disappointed me and always had my quilts done when she said.
I think you need to have a heart to heart talk with her and if she cannot commit to s specific time then I would simply look for someone else.