So, in a land of myth, and a time of magic, the destiny of a great kingdom does indeed all depend upon a silly girl?
Except, it wasn't half as bad as I expected; in fact it was one of the best episodes yet IMHO. She wasn't a silly girl at all, she was a deep and well thought out character. She believed that what she was doing was right and just, just as all freedom fighters would. One man's terrorist is another man's freedom fighter and all that jazz. Pity we had never seen her before today.
I agree about the idea of fate - and that whatever Merlin did he could not change the events unfold exactly as he predicted they would. He was watching a car crash in slow motion from the other side of the road.
The ending was another step up, but I was waiting for Morgana of the tatty hair to just laugh and say "Who? Merlin?" I still can't believe that Arthur will die in two weeks time - he hasn't achieved anything yet, has ruled for less time than his father, and still only Morgana is aware that Merlin is some great wizard. Surely, Arthur must rule, and Merlin must practise magic for a fair few years yet otherwise why would they be remembered?
And in my TV guide letters page, someone has complained that this Season is too dark! Apparently, they liked the humour in it before. I'd make them watch re-runs of The Chuckle Brothers back to back as a punishment for that.