Is there a way I can gain authority to mum's affairs as everything is in her name?

Yay! Real help! lol! Glad you came along, CM.

Stillperfect ~ Any additional details you're comfortable with providing - such as your location, what's happening with mom as far as medical history and living situation - all of those details can go a long way towards getting better advice on this site. It does seem that legal guardianship of your mother is what you're seeking. :-)

austguardianshiplaw.org seems to be the site you want. Oh brother. There are, apparently, eight entirely different sets of regulation - one for each state, I suppose? Hope something there is helpful, anyway. Hugs.

I saw your answer on my page just now. If your mom has severe dementia, then a doctor will have to assess her and make a medical determination. That medical determination will be taken to a court of law to have your mother declared legally incompetent, and that will then set up the need for someone to act as her guardian.

In my major U.S. city, there is a Probate Court location that deals with all-things related to estates, POA, guardianship, conservatorship, etc. They have people on site that will give you the correct forms to fill out and also offer some basic legal advice how to proceed.

You can find that basic legal advice online, too. I found this how-to list just now:

"Here are five general steps to follow to get someone declared legally incompetent:
File for Guardianship. ...
Consult an Attorney. ...
Schedule a Psychological Evaluation. ...
Submit the Evaluation to the Court. ...
Attend the Hearing."

After the declaration of incompetency, you would file for guardianship of your mother.

There are Q&As throughout AgingCare.com that address these issues. :-)

But, basically, if your mother has severe dementia and doesn't have POA in place, you would need to obtain guardianship of her. I wish you the best.

Why is it too late for POA? The next step depends on why your mother cannot give POA.