I am not aware of any genetic predispositions in Great Danes that would cause bone abnormalities. I also just researched this on our online database, VIN, and found nothing.
Depending on how old she is, she can develop bone pain from swelling of her growth
plates. However, this shouldn't cause her bones to be abnormally spaced. I honestly can't say what this is without looking at the xrays. Also, sometimes, they can have one side of the leg grow faster than the other (this is more common in large dogs) and this would cause her gate to be abnormal. I am not aware that this is genetic, but an orthopedic surgeon would be able to better diagnose this. Some dogs do outgrow this with age, but sometimes they need surgey to correct the inequality of growing. Another possibility is that she has a tendon contracture (this is something foals can get), and this can potentially be cured with a special spling/booty for some weeks.
I would encourage these owners to have an orthopedic surgeon evaluate her and the xrays for a definitive answer. That way, you will also know if it is just an odd-ball, temporary issue or if it might be something genetic and more serious (however, I think that is less likely).
I hope this gives you some direction. Thanks for being such a responsible breeder!