Are you considering removing your child from school and educating her yourself without the involvement of the Local Authority? If so, I'd recommend trying other forms of home education instead of online school. As many families discovered during the pandemic, younger children (and often older people too) tend to have trouble focusing on online lessons.
There are many many ways to educate. For example, you can do project-based learning where you cover all subjects through projects. So, if your child loves fashion design, you can learn history, English, maths, art, and politics by studying fashion design. Some families like mine do hands-on learning through play, in which the child decides what they want to learn and when; in this model, the adults help the child find resources rather than telling them what to do.
Some kids - mainly older ones - like to dip into short online courses on subjects which interest them. I hear the £2 Tuition Hub is good for that.
You might like to make contact with a local home education group to learn about educational opportunities in your area (museum exhibits, special events, etc) and also so you can get support for yourself. Even if your child cannot manage to be around other kids just now, if you have someone to look after your child, you could get together with other parents to talk about home education and get some more examples of different approaches you could try. Your child isn't alone in finding school overwhelming, and it's likely you will meet other parents who have removed their kids from school for similar reasons.
One common piece of advice, especially if a child has had a traumatic time at school, is to start off with a period of recovery. During this time, encourage your child to do whatever makes them happy, with no academic demands on them. This doesn't mean they will be getting no education, as they are learning from everything around them. Once they have started to feel better, they will be able to engage more with formal and informal learning. For kids who aren't in a large-group educational setting, there's no such thing as falling behind. They just do everything as they are ready for it.
Good luck!