And yes, a good confo shot or two and video of her moving (preferably under saddle), will do a lot to help us give you a figure.
But yeah, area has a lot to do with it. In some parts of the country a certain horse could go for twice what it would go in other parts.
You will definitely have much better luck selling her, I'd think, if you include good pictures and video in the sales ad. I'd assume many people are like me and probably won't even look at an ad if it doesn't have some good pictures, at the very least ;)