I think to answer that you would have to clarify for me in what way the girl constitutes a threat to the other children?
And we go full circle. The risk, to me, is self evident.
This is a child who has the capacity to falsely allege sexual abuse against a 7 year old and 16 year old, to falsely allege violent abuse at the hands of the OP and to have the capacity and life experience to falsely allege that her own father held a sword to her throat and threatened to decapitate her.
Is it really the case of "no harm, no foul?" Am I right in my reading of the posts here which imply that not only the OP, but the other DCs, who are old enough to understand the nature of the allegations made, are expected to forget about it, because after all, their names have been cleared, so no harm done?
I have limited experience of child abuse investigations. It's unpleasant and distressing for all involved. Threads on MN make it clear that when an adult maliciously instigates child abuse investigation proceedings, it is considered child abuse on the part of the adult. The children involved are subject to intrusive, invasive and sometimes life-altering experiences. An adult forcing that on a child unnecessarily is emotionally abusing the children involved.
Yet when a child makes false allegations, it is considered harmless to all the DCs?
And as I said up thread, this DCs capacity to imagine and allege the degree of violence that she accused her father of is alarming to me. In a culture in which weapons and violence are more commonplace than here in the UK, the casual attitude with which the DC referred to murderous violence, with apparently no awareness of the severity of her words, would cause me of fear for my and my DCs safety were I to share a home with her.
I think the OPs DP is disregarding a very real risk. If the OP returns to the thread to clarify whether the family are receiving therapy and support then I may well reconsider, but without that in place, the OPs fear is well placed IMO.