Kolo, I'm so glad you're on this thread, along with others who speak sense.
OP, when I first saw your post, I thought, 'Yes, rip them up, show some solidarity with her', but in light of what others have said, I'm not sure. It probably won't help in the long run, if you undermine the school and the system, bad as it is.
The most important thing is your daughter's self-esteem, imo, and she needs to have some hope of success, some feeling of agency to carry her through her secondary schooling, or she could risk becoming disengaged and fed up, and wasting her time. But you sound like a lovely parent, and she knows you are on her side, which is far more important than anything else.
You might have to do some damage limitation (especially when other parents or children boast about their results).
I think the best thing to do is simply to behave as if the results are of little or no significance. Tell her what other posters have suggested, and that you are proud of her anyway, for the lovely person she is and how hard she has worked, and there's more to life than SATs. You can always tell her how you were a late developer, to reassure her that her future isn't all decided at age 11. Maybe even ask her and/or her teacher what she finds most difficult and see if you can help her at all - but in the spirit of 'we can do this if you want to give it a go, but you'll be fine anyway'?
Ignore her results, or 'forget' about them unless she reminds you, or ask her whether she wants to know them. Show her how little you care about them, and how much more you care about her. Good luck.