I found out my sister, who was on Medicaid, had a pension after she passed away. What should I do?

The thing is the pension doesn't pay out till retirement. There is no way that Medicaid would or should have known anything about it. The pension was not being paid out while she was alive.

"Medicaid benefits received on or after age 55 are subject to estate recovery."

I guess you told the Company ur sister passed. Are they willing to pay out in one lump sum? IMO this is part of her estate and now an asset. Yes, you need to talk to an elder lawyer well versed in Medicaid.

If the pension was never paid, it’s not a problem for you – you have nothing to repay. I’d inform Medicare and let them deal with it. I'm sure they will be willing to claim it from the company!

Where was her pension being deposited?

No will...no estate. I realize POA ends at death but I am still the person responsible.

I will contact an elder attorney.

I’d see an elder attorney. POA ends at death. If there is a will, the Executor needs to handle the estate (and the pension issue).