Immediate memory loss.

In my story, my main character has immediate memory loss.

Now I'm not sure whether or not to have it as a spell to make her have memory loss straight away or there to be an accident that could do this to someone.

My question is can someone (with magic, seeing as it's a fantasy novel) forget the first ten years of their lives? My character doesn't remember the first time years of her life, and it's been seven years since then. So she's seventeen. But my question is, can there be some sort of accident like a bump on the head or something else that can make some lose their memory loss immediatly?

If you can answer this, thank-you so much.

Thanks guys.

I've decided that maybe since it's a fantasy novel that maybe it should be something supernatural that does it. But I'm going to mix both, if that makes sense. Kind of like the ECT and a spell put together if that makes sense. Thank-you though.