The answers to your concerns are contained in your message. You are intuiting that you need to let her do it her own way even if that means squeaking by or failing. I would encourage you to do just that. When you stop paying attention to her misbehavior and only respond when she does do well, you will throw her out of kilter! My guess is she will try hard to get you involved again, but if you just remind her that it is her choice, she will most likely do what she needs to do to pass. Better that she fail now than in high school, where she loses credit.
You have reason to fear that if she continues in her study patterns she will have difficulty in high school. She will. But you've already realized that for your own emotional and mental health, and for her growth, you can't micro manage her.
This will be your greatest difficulty -- to let go and to expect her to succeed without you. You can do it.