Just to be sure, as you are a mum, but not the
mum are you fostering/adopting these two children?
Once the folks on the Kent section have finally sorted out what the qualifying marks are this year it will be clearer how much ground you have to make up at an Appeal.
Are there any CATs test results or other test results that the school can provide to demonstrate her ability? What did the end of year school report in July look like?
I suggest that you speak to the current Head and discuss her performance at the current school, and also find out what sort of record they have of her achievements at the previous school. If the Head is willing to give you strong support, that will be a good start.
The disruption and uncertainty over the last year will have certainly affected her academic performance. Likewise, if she knew that you fighting for custody on the day of the tests, that will undoubtedly have affected her too.
The circumstances will certainly be taken into consideration by a panel, but you need to present them carefully. Please never forget that a successful appeal is 90% academic evidence and 10% mitigating circumstances, no matter how traumatic they are.
If you haven't done so already, please also read Etienne's Appeal Q&As - there is a link at the top of this page.
Once you have a little more information please come back and we will do all that we can to help you.
P.S. I have just noticed that Etienne was posting at the same time as me, but I'm posting this anyway! You now have both of us on your case - "Buy one free, get one free!"