Can someone explain to me who Anna Buckingham is?

I am very excited about the upcoming show on Showtime rightfully dubbed "The Tudors." However, I wanted to get a little more information on this show so I went to www.imdb.com. I was looking at the cast of characters when I saw a name I didn't recognize being that of a Anna Buckingham. I am currently reading The Six Wives of Henry VIII by Alison Weir and I certainly haven't come across a historical figure yet by that name. Is there something I'm missing? Who WAS this girl?