What to do when a professor agrees to write a recommendation letter but doesn’t? I’m applying to grad school and two weeks ago I asked three people for recommendation letters, two from employers and one from the professor. There’s no specific deadline, but I’m hoping to get accepted quickly in order to be eligible to start classes in the fall. Now, my entire application is complete, except for the one recommendation from my professor. I sent a follow-up email, to which she said that she’ll complete it in the next two days, which was great. But it’s now been a week since that email, and nothing’s been submitted. I sent an email responding to that saying thank you and offering more info if necessary, and have not heard anything back. What should I do? Should I wait, email her again, or ask someone else? I have some other people I can ask, but the problem is that I have no way of accessing the link as the university sends out the link with the application. I don’t mind waiting at all, but my concern is that if the professor decided to back out of it and I have to ask someone else, I want to give the new person as much time as possible by sending them info now. Help?
Ask someone else now.  Provide a specific date, e.g. June 10, by which you need the reference and explain why.  You can almost certainly add another referee to your application.  If, for whatever reason, you cannot add another referee, cancel the one that's outstanding as soon as another professor has agreed.

If you can add a referee without canceling one, write to the professor who has already agreed and give her a deadline, also explaining why.  (NB: Professors are necessarily pretty good about meeting deadlines, and often abysmal at those things that do not have deadlines.  This from extensive research on a sample of one, namely Yours Truly.)