EHCP - parent or school submission best?

We’re in the process of requesting an EHCP needs assessment through the school for my 8 yo daughter. 

We have been advised that because she goes to an independent school, a submission by ourselves as parents might lead to a better outcome. 

Does anyone have any experience of what is best? I just want the right provision for my daughter who is in autistic burnout and unable to attend school most days. 

Thank you for your help