Confused/concerned about Maintenance Loan awarded

So my niece has been applying for student finance as she is hoping to go to university in September 2021. We've had alot of hassle with the application process and its very much affecting her mental health.
The issue is my niece has been living with her grandmother for approximately the last 4 years after her mother passed away in 2014. Her dad has never been in her life, and isn't even on her birth certificate, but because she has recently started talking to him (to find out more about possible siblings/etc) its required that he supports her application. But he has no legal responsibilities for her, he gave them up when she was 18 months old. Her grandmother has been her legal guardian for the last 3 years, but student finance will only accept support for the application from her dad. And with them only just talking, and him not even being on her birth certificate its not something she can really bring up with him. Customer services give different advice every time they have been contacted and its left us confused.
She's been awarded a low amount for her maintenance loan which we tried to appeal (i dont know if we've done it correctly) but that has been denied. But if it stays as it is she is going to struggle to afford to go to university as it wouldn't even cover her rent for the year and her grandmother can't financially support her with the money she would need due to being in receipt of benefits.
So really what I'm asking is could you explain why this is the case as it has confused the household (auntie, grandmother and the applicant). We've never been asked for any evidence to support the claim at all (except for her dad to support her claim), and due to not living with her parents she was forced to fill out an estrangement form which was also denied. So would it be possible to have an explanation and breakdown of why this would be the case, and why her grandmother can't support her application as she is her legal guardian.
We were told that if we got her father to support the application that would be acceptable too, and may change the decision, however whenever we try to fill out his section to support her application it won't come up online as an option. Is this because the funding amount has been decided and if so how would we get past this blockade? Thanks.

Hi there, this is due to the government regulations.

https://www.legislation.gov.uk/uksi/2011/1986/schedule/4

To apply for the higher rate of funding, her dad must support her application unless she is estranged from him, and in that case she can ask a professional person to complete the estrangement form http://ow.ly/d/8pcZ

Thanks, Isaac

How can she get her dad to support her application? She tried doing it online but it would not let her, is this because she has already been awarded a set amount? How else could she fill it in?
Thanks