If it's a) then we'd want her to stick with it and work through it... after all, perseverance, effort, and even failure are critical lessons that she's not had to really learn yet. We don't actually care if she comes out of the class ready for the test or even having retained most of the material. For us it's about the effort.
I agree with this up to one point - from my perspective, it's not about the *effort*, it's about the learning, acquiring knowledge. I wouldn't want to quash my child's someday-potential-passion for this particular science subject by forcing them to stick with a class where the effort required was so huge it was causing issues. I'm not saying I'd let my kids back out of a class simply because it was hard, but there's a difference between coping with a difficult class and feeling constantly behind and frustrated because of having to put in a relatively extreme effort to stay on pace. I have no idea where your dd and this class fall related to those two things, but that's what I'd be looking at in making a decision.
Best wishes,
polarbear
