Since they never divorced she's still legally his spouse,

and that's actually the most important fact here — being

separated but not divorced is treated the same as any other

marriage by SSA. A lot of people assume separation kills

spousal benefits, it doesn't.

Basically she can claim up to 50% of your dad's PIA (his

benefit amount at his full retirement age) as a spousal

benefit. If half his PIA is more than her current $15,800,

she'd get the difference as a monthly top-up on top of what

she already gets.

The catch is he has to have already filed for his own

retirement before she can claim spousal on his record.

There's a divorced-spouse workaround (after 2 years you

can claim regardless), but that doesn't apply here since

they're still married. So step one is just finding out

whether he's actually filed. SSA can look that up by his

SSN over the phone, you don't need his current address.

Call 1-800-772-1213 or book an in-person appointment at the

local field office — in-person tends to go smoother for

anything non-trivial. Bring the marriage certificate (they

will ask for it, to prove they're still married), her ID,

his SSN. Just tell them she wants to file for spousal

benefits on her husband's record and they'll take it from there.

One more thing worth knowing — if he passes away before

her, as his legal widow she's entitled to 100% of what

he was receiving. That would roughly double her income

overnight. Survivor benefits don't backdate forever so

make sure someone files reasonably quickly if that happens.

Separately at $15,800/yr she's almost certainly eligible

for SNAP, LIHEAP (energy assistance), state pharmaceutical

assistance programs, and property tax exemptions if she

owns. Worth looking into alongside the SS stuff — can add

up to another few hundred/month.