Can someone be counted as a companion if they only appear in one story? I’d argue they can’t, but apparently Astrid Peth from ‘Voyage of the Damned’ was definitely conceived as a companion. Here are a few very brief quotes from Kylie Minogue about her role as Astrid, and her acting career up to that point.
I went into Neighbours at 16, was probably a good actress at first, but I did dodgy movies like Street Fighter (1994). Everyone makes mistakes, and I’ve made enough.
I’ve got a low boredom threshold and jump at opportunities. ‘Doctor Who’ goes back to my roots as an actress. At the read-through, I tried to look cool, but I was petrified. Then, on my first day of filming, I realised I was in my spiritual home. I’ve a lot of affection for Astrid. She’s a waitress, a dreamer, alone, and she wants to travel. Perhaps that’s like me when I was younger, but I had opportunities. She’s still struggling.
Doctor Who Interview Archive 