It's true that your grammar and dialogue s sometimes a little off, like you said, but I really love the story. It's beautifully tragic and a great way to introduce this character. Stories like it have been told many times before, but I think it's the sort of thing that can resonate with someone even if it's familiar. We've all felt that desire to bring back someone we've lost, and when dark magic gets involved, it never fails to be a tearjerker. Good choice of music, too- I've never heard of Rozen Maiden, but I do like the melodies, and they suit your story well.
Your art is simplistic and the animation is very limited, but I think that's the proper kind of art for a prelude or prequel story. The typical "anime" look isn't especially original, but again, it still works anyway, and it looks a lot cleaner and prettier than a LOT of other amateur works. You may not believe this, but I'm actually VERY pleased that you actually drew the mouths properly while in profile. A lot of people - even some professional artists! - have a tendency to just draw them on the cheek, which irritates me to no end.
I look forward to seeing more of this story. "The Grand Witch" is a pretty good setup and I bet that the plot proper will be even better.