My top tip is, do it now. Don't wait. Two reasons:
Your daughter is so overwhelmed by school she won't be managing to learn much. All of her energy is wasted in fear and stress. Even when she isn't at school, she may well have such high stress levels about school that it dominates her life. The sooner you can get her out of there, the sooner she can start to feel better. Good mental health is priceless, and what's more, once she's happier she will learn better.
Second, you should know that GCSEs (if she does them. She doesn't have to. But most home ed kids do) are tricky to arrange. It's a complicated thing for parents to master, but luckily other home ed parents will be very helpful. You can figure it out, but it takes time. By starting home ed now, in Y7, you can have an easy, less stressful transition. You and your child have a few years to explore and learn without worrying about choosing exam subjects and methods and deciding when and where to sit them and facing deadlines.
Don't leave her in school much longer. If you do, you may face the double whammy of even worse mental health combined with exam stress. (As I say, she doesn't HAVE to sit exams, and if she does, it doesn't have to be at the same age when her schooled peers do them. But many teens have had it drummed into them at school that education is all about GCSEs, and they may feel like failures if they don't do GCSEs at 16 like "everybody else".) By taking her out now, you give her time to recover from school and have some fun before starting to think about exams.