Here's a clip I found (I remember watching this all those years ago!) of episode 1, series 1. Felicity appears about a minute in - there's lots more on YouTube if anyone's desperate. I don't know if Worst Witch was aired in America, but she played Ethel Hallow: basically the school know-all who was more than a little bitchy!
i just wanted to say that i thought she was perfect in northanger abbey. i was worried about how they would film this one since they clearly were trying to modernise mansfield park but i felt felicity jones was wonderful in her role of catherine morland-catching not only her vivid imagination but her realisation of the consequences of this. i cant wait to see her in more roles