Am I entitled to her unclaimed benefits?

Probably not if it was a pension. Only spouses may be able to claim those benefits. If it was an IRA or a 401k then you may have benefits due you. Talk to an attorney.

You need to speak to the pension administrator and get a copy of the summary plan description. You may need the assistance of an attorney to fully evaluate the options available in the plan and what vested rights your mother had. Your mother's estate may have a claim.