Well, it's like when you think about how people in the past hundreds years were able to do some things without the actual technology. They were creative, inventive and tough. Equines have strong necks, but not enough for something that long. Also where to put the scabbard to be not obstructive how she would pull or put it back in it. But since it's a commission, you must have just drawn what was asked, right? So, she should have a short sword with a scabbard tied on her side. That's just an idea. That doesn't diminish your awesome work on it.