If my mom is the only living full-blood relative of my deceased uncle, what steps does she take now?

Sorry to hear about your mother's uncle.

Intestate means dying without a Will.  Inheritance is determined by the rules of intestate succession.  Since your mother is her uncle's only survivor, she would inherit the estate.  The estate you described is too small for probate.  Your mother should contact the bank where her uncle's account is located and ask what documentation they will require for her to obtain the funds in the account. Your mother should have had more than one certified copy of the death certificate prepared. The bank will need a certified copy of the death certificate.  Ask if they will require an affidavit of a small estate without administration.  That affidavit (declaration) will establish her right to have the funds paid or transferred to her.

At the law library, look in the index of the Probate Code under small estate without administration.  Look for affidavit.  That will give you the form language of the affidavit.  After the affidavit has been written, it should be signed in the presence of a notary.  Another reference source at the law library is Pleading and Practice.  Look in the index for small estate without administration.  Then, look for affidavit.  That will also give you the necessary language to include.

The steelworker's retirement probably terminates upon death; however, it would be advisable to contact the company to find out if there are any additional benefits that your mother as her uncle's survivor may be entitled to receive.  If there are additional benefits, ask what documentation the company will require in order for your mother to receive those benefits.  Ask if they will require an affidavit of a small estate without administration.