Jane was really stellar in the role, I thought. She's sweet in one scene and vicious in another. Weepy and upset to angry and mean. She's happy and sad and bubbly and just all around fantastic. I really enjoyed seeing her performance--it was an unexpected delight to see an actress I'm so very fond of show up in a show I already watch. Usually I have to track episodes down but this was a surprise!
Anyway, the episodes were called "What Ever Happened to Sarah Jane?" parts one and two, and if you're a fan of Jane Asher, I highly recommend checking them out.