Honesty is the Best Policy
She responded with a very nice email, commending me for recognizing that it was better to bow out and focus on those things that are currently more important. She is teaching the course this summer, and I fully plan to register for it again-it is a fantastic class. The way I look at it is that I've now completed half the readings, I can do the first two module's assignments right at the beginning of the semester, and if I don't get to read the rest before the summer session, half the reading over ten weeks isn't too bad.
So, I felt good about being honest.
An hour later, I got another email from her. She is currently hiring for what I do and suggested I apply. Somehow, I don't think that I would have heard from her if I had just dropped the class without the email.
And if the job pans out, it won't be the first time that I interacted with someone in a professional capacity and then later got a job from that acquaintance!