What bank would be a good recommendation to set up a separate account for my mother to serve as a Fiduciary to manage her VA funds?

Navy Federal Credit Union

https://www.benefits.va.gov/fiduciary/fiduciary.asp

Also, if you go to your local VA and speak with a social worker, they’re usually pretty good about facilitating this type of stuff.

I don't know your entire situation, but I am a BIG fan of local credit unions. Where I am currently, we have Fortera Credit Union - which used to be Fort Campbell Credit Union. They are not military exclusive, but they are very familiar with military, which helps some things along.

Out of curiosity, how is your mother receiving VA funds but NOT eligible for USAA? If she is receiving VA funds based on her own service - USAA eligible. If she is receiving as a widow - still USAA eligible!

I am also a big fan of setting up linked accounts. My wife and I both have separate accounts at our Credit Union, but I can send her money direct from mine if I need to. If I were you, I would look at setting your mother's account up at a bank where you already do business and link them, so that you can transfer between the two easily. This helps in case something happens to lock her account, you can use yours and recoup later (or if hers is only locked from debits, but not transfers - it has happened to me before - you can transfer to yours and then just pay from your account), or if hers runs short for some reason (not that the VA would EVER screw up pay), you can funnel from yours into hers to help her out.