Hi Owls!
Really sorry to hear your dd had such a rough time at school. Is she out now? How is she feeling? I think the top priority in the short term is to help her relax and recover. She'll be able to focus much better once she is happier. And you have plenty of time: I assume you are planning to HE at least until Sept? Kids learn very fast with one-to-one attention, and education targeted at the right level for them. Besides, much of the school day is a write-off in educational terms since there is so much "overhead" for moving between classes, waiting for people to get themselves organised etc etc. You'll be surprised at how much she can cover in just a few hours a day. That means you can let her have a few months off with no fear of her falling far behind.
I do have a 16yo who is HE, but our own personal experience is not very relevant to you because she has never aimed at joining school and isn't doing exams at this time. I hope somebody else will come along soon who can give you more specific advice.
Meanwhile, I can give you a bit of information and my impressions as a bystander at lots of chats among HE friends about such subjects.
It seems to me that many people both in and out of the school system regard years 7-9 as a time when relatively little education is accomplished in the classroom. (No doubt a secondary teacher will wander through in a minute and bite my head off for that one!) "Consolidation", if we want to put it more tactfully. Ensuring kids are all on the same page and ready to start working toward GCSEs, giving them independent study skills and so on. Regardless, the fact is that many home ed families don't get down to serious work until they start working toward exams. So you don't necessarily have to do much in order to keep up.
My HE pals do seem to be interested in developing the following skills at ages 12-14:
Foreign languages. If your child joins a school in Y10 where the others have been doing French since Y7, and she hasn't, she may not be ready/allowed to choose it as a GCSE option.
Essay writing. Useful if she is going to do exams whether at school or not.
By the way, looking toward the future, it is considered fairly easy to rejoin school any time up to the start of Y10. After that it gets increasingly difficult for the inflexible, rigidly age-based school system to accommodate new arrivals. You might want to bear this watershed in mind. If your daughter is still home educated after that time, in effect you'll be committing to carry on with HE. On the plus side, if you do HE for exams then you can do any number of exams, at any age and in any order. Most people opt for IGCSEs but there are alternatives. HE is far more flexible than school, which might make it an appealing option.
The only sites I know of are BBC bitesize (which I've never used, but people say it is good and engaging), and Duolingo, which my teen and I have recently started using for learning a foreign language.
If you have questions about specific subjects then you may get a good response by asking here on this board.
Good luck!