The school nurse should have reported it to SS within 24 hours and then SS have 7 days to do their initial assessment. It doesn't seem to match what has actually happened in your case HAW, but then again you may not have been fully informed by the various agencies, and I really don't think it's a good idea to put too much detail on this thread.
This is why I think you must talk it over in detail and in confidence with a trained person. You can arm yourself with info from the internet. That Devon website seems to have detailed, comprehensive, up-to-date information on it.
If your dd maintains that what she has said is the truth, you would be quite wrong to encourage her to drop the charges.