Hi Sterling
I believe you are asking about SS insisting that your mum is discharged from hospital to her own home with a care package in place because they consider this is appropriate and this must be tried before considering full time care, when the medics and you can see that this will be unsafe and your mum needs to be in full time care ie a care home
I don't think it's enshrined in legislation - but it does seem from postings here that it is increasingly seen as 'policy' or required procedure - whether by some LAs and/or SWs - especially if the LA will be funding the care
I guess you are trying to find means to fight for your mum
I really do wish you well
and hope someone else can offer a more informed response than mine