First, don't worry about finding the perfect person. I think that if you have the qualifying numbers, you are pretty much in. Second, 45 minutes a day is plenty of time, especially over the course of a school year. There is probably at least one middle school teacher who thinks highly of your DD - you need to ask her specific questions about all her teachers. We used a current teacher just so everything was fresh, etc. While DS was in mid-elementary so his Nominator was his homeroom teacher, DD was in 7th so we used one of her middle school teachers. It is a bit harder when you have many to choose from but I started with the teachers who have nominated her for various school awards/honors, then gave preferences to the ones from the current year and who were enthusiastically vocal (to other teachers and students) about DD's work products. I think you go with a teacher who thinks your DD stands out from the other students in his/her classes.
Good luck but you really don't have to worry - I think it's really a question of hitting the numbers.