Help me me identify a Dr Who Society Film

I had a very interesting conversation with my nan yesterday. She told me she had been in a Dr Who Society film/episode, that stared Elisabeth Sladen and a doctor but she cant remember who. It was filmed at Peckforton Castle in Cheshire and I want to say maybe late 80s or early 90s? It's was a medieval themed episode.

Does anyone have any idea what this was? My nan really wants to see it again! Thank you in advance