My stepmother was married to my father for 2 years and 5 months when he passed. There were no children of their marriage. My father was in receipt of a private pension and on his death my stepmother started to receive a widow's pension. She has now remarried.

I want to know whether she is still entitled to a widow's or state pension since remarrying and if not, who would be entitled to the pension now ?

Yes, she was the beneficiary of your father's pension. Her remarriage doesn't change that.

She still gets it, unless there was terms in the contract about remarriage. ( and I doubt there would be)

I have to ask why is this in question ? Are they denying her the payment ?