Hole in Navicular Bone... Any Info would help!?

How did the "hole" occur? There is not enough information here. From what you said, you should p on this horse. She would not be able to perform like you want her to do. Aside from that, maintaining her when he has problems will be very expensive and she will be probably retired to the pasture at best. "sound since November" means nothing. She could be drugged. You need to be very careful in this situation. No way would I take this horse on except as a rescue effort which is what she sounds like she needs to be. The eggbar shoes are horrible for the horse and the fact that the owners feel it is necessary to use such a horrid shoe to present her as sound tells me she is in big trouble. Just because they can nail these horrible shoes on and present this horse as sound for a brief period to you does not mean she is sound. Take the shoes off, trot her out on rough ground and see how she does. I would suspect this horse is highly medicated when she is being presented. No No No , Move on, Run away. Avoid like the plague unless you can come up with more positiive information.