Ah! Someone beat me to it. Hilly (short for Hillary) is just so CUTE as Tennant's Doctor nd her sister makes a very convincing Donna Nobel. They also did a music video with Hilly as Captain Jack Sparrow from "Pirates of the Caribbean". It's uncanny how well she captures his body language and expressions.
And yes, do check out the "making of..." video and Hilly's video diary. She was sick as a dog the day of shooting the big stage dance number...which continued until 6:30...the next morning! Poor girl saw the clock and was so out of it that she assumed it was PM, not the next day. Now that's a trooper!