Are you talking about the line near the lateral heel that runs up to the quarters? It's hard to tell in the picture, but it looks to me like her sole has shed from that area to revel new growth. I would keep an eye on that area though, as it looks like there may be some bacteria tracks forming on the actual wall. Most horses have straighter medial hoof walls, with more curved lateral walls - it doesn't look too out of the ordinary to me.
Lamellar wedges form at the toe as a result of a laminitis/founder episode - from the underside of the foot, the toe will look stretched out, often with the white line area appearing very thick and brown or red in color.