Series 2 (Doctor Who)

I have been confused by this ever since I watched the series 2 finale. The actor who plays Martha in series 3 and beyond is there and she is converted and also works at torchwood but then in series 3 she is working in a hospital. I don't think they are the same characters but it's confusing can someone tell me what that is?

It says on the page for Attack of the Graske that it’s available on the Series 2 DVD. Can’t seem to find it on my copy. Any help as to where exactly it is?

Here's my ranking for Series 2, including the Christmas Special. Not including minisodes.

1) Episode 4: The Girl in the Fireplace

2) Episode 13: Doomsday

3) Episode 12: Army of Ghosts

4) Episode 3: School Reunion

5) Episode 9: The Satan Pit

6) Episode 8: The Impossible Planet

7) Episode 6: The Age of Steel

8) Episode 5: Rise of the Cybermen

9) Episode 11: Fear Her

10) Episode 2: Tooth and Claw

11) Special: The Christmas Invasion

12) Episode 12: New Earth

13) Episode 7: The Idiot's Lantern

14) Episode 10: Love & Monsters