the love of a good character

I'm writing Isabel's point of view today and finding it hard going. Why are some characters so much easier to write than others? A question for the ages, and one I don't have an answer for. It's not because she's bitchy, because I can find quite an enjoyment in writing a bitchy character. You get to put in the character's mouth all the things you long to say to people who annoy you, but that you don't say because once you were a good Catholic girl, and you're stuck with certain behaviors.
In another novel, I had a difficult character, and the difficulty lay in my knowledge of her: I just didn't know enough about her, even quite far into the book. And this might be Isabel's problem, or mine with her. She disappeared from Logan when she was a teenager, and her past is something of a mystery to the other characters in the book--she wants it that way. But, of course, it shouldn't be a mystery to me, and it is.
Maybe we need to get together over a drink and thrash it out. Maybe I need to write a journal for Isabel (except that she never would). Or a blog--what would Isabel blog about? Or maybe write an unconnected (to the novel) short story that would take on Isabel's past. I have a good title that's been banging around in my head, "Isabella, Queen of Spain," and maybe I'll use that, although I'll have to figure out what Isabel has to do with Spain. There's nothing to beat the pull of a good title though--sometimes, a great title can draw you right into a story you didn't know existed.
Did you know that when Columbus died in 1506, he still believed he'd found Asia? A warning to explorers and writers everywhere.