Legal Question in Elder Law in California

You don't need Letter's Testamentary - that's what you get when you file for probate, and in this case, probate isn't needed as the account (and presumably all other assets titled solely in your uncle's name) is less than $150,000 in total.

What your aunt needs is a declaration made under "California Probate Code section 13101". If you google that phrase you'll find the declaration online. Your aunt can fill out the form and sign it before a Notary Public. Then she should take the form to the bank with a Certificate of Death.

Please note that she cannot sign the form less than 40 days after the date of your uncle's death.

Also, your aunt ought to review the trust, and all of her assets, with a trusts and estates attorney to make sure that everything will be in order upon her death.