I wouldn't worry too much about that yet. Shoot, Rafe was over a year old before he started showing withers. Even if she does end up mutton withered, the only problem is it makes secure saddle fitting a little harder. If you don't do any roping though it won't be that big of a deal. Dobe is mutton withered and the only time it's really a problem is when I drag stuff, I always have to readjust the saddle after a heavy one.
The only thing that I see about her that I really don't like is she is a bit straight through her hocks but there are a ton of horses out there that are like that too.