Sif is difficult for a first playthrough, especially if you haven't played Demon Souls. Don't be discouraged! Its just a matter of learning how/when to roll.
Also, don't skip any areas on your first playthrough. You only have one chance to experience the game freshly.
I did beat Demon's Souls, but Sif is still a challenge. Anyway, I don't plan on skipping or missing anything. I will just come back here when I am a little better equipped. AKA, when I get my Claymore +6 up to a Lightning Claymore.