I don’t think the problem is the C’s. Someone more savvy about the schools on her list can weigh in on whether she needs another safety school.
I think something she needs to tackle is attitude. College classes move VERY fast compared to HS, and if her response to not understanding something in HS is to ignore the problem until the midterm or the final- that’s not going to lead in C’s in college, that leads to dropping below the minimum GPA required to be enrolled.
I wouldn’t worry about a kid with the occasional C who knows to ask the teacher for help, who goes to the tutoring center, who has formed a physics study group with one or two of the stronger kids in the class. I’d worry about a kid who thinks that because she’s not a strong natural math student, somehow she can fake her way through it. This is not going to cut it in college.