I'm not great on WB bloodlines (just learning them myself) but from the pictures, it seems like all the riding pics are her in some sort of draw or side reins so I can't really get a feel for her movement. I'd love to see some of her at liberty as well as her under saddle without any artificial aids - that right there would present her as a more valuable horse and less green. I'm not saying misrepresent her - I think you gave good honest information, however if you have pics of her only in side reins/draw reins, it makes me wonder how good of a mover she really is since with artificial aids it is hard to see how the horse actually is moving (especially since she isn't really carrying herself at all in the pics). By adding a liberty pic it would give a feel for natural movement w/o a rider - which should be nice based on her breeding - and thus justify the asking price (whatever that may be).
I think a good general assessment is depending on her bloodlines, between $6k - $10k. I know that's a HUGE range, but since I'm not well versed in WB lines, I can't say any more specific than that. I think a lot of people expect to pay in the 5 figures for a well bred WB, even a green broke one, provided they are level headed which you say she is.
I did a search for Tx Oldenburg on Equine.com and a 3' hunter is going for $13k and a 2008 gelding is going for $8.5k. There's also a 2005 mare advertised for $15k as a hunter prospect. So that should give you an idea for a comparison. I'd say some of the negatives are her lack of training and age so if you can get some saddle time to refresh her memory so she's not so rusty, it would likely be easy to get about $10k for her is my guess. Good luck!