Which antibodies were elevated?

There's a somewhat new disease called Hashimoto's Encephalopathy, where the thyroid antibodies are elevated. it is treated with steroids and other immune suppressants and IVIG, etc

There are also a lot of other obscure and not very well-known diseases in the same family of "autoimmune encephalopathies".

There's a good article on it if you go to pub med and type in "autoimmune encephalopathies". If it has too much medical jargon, then maybe bring it to your mom's neurologists and ask if she's been checked for these.

I am sorry your mom is so sick and undiagnosed!