Yes calc is for 12th grade. I would ask the teacher if she should stay or do they have a regular level offering. Ask if there Is there a way to learn the material she isn’t grasping. Maybe you can hire a tutor. It’s unfair to say because a student doesn’t get an A that the teacher’s grading is an issue. Not everyone can be or needs to be perfect.
This statement below is a little perplexing and worrisome.
“How bad would this C affect her over all chances of getting admitted to a good college?”
One C or 5 is not going to keep her away from a good college of which there’s likely hundreds. Please don’t fall into the UC or high US News ranking trap. As a sophomore you don’t know how her record will be ahead but assuming she’s an A/B l and occasional C student going forward, there will be tons of great schools for her. She needn’t stress herself with UC or bust.
Life is full of pitfalls. This is not a major one.
Good luck to her.