Horse mane and tail won't grow?

One of the horses I am concidering buying is perfect except one thing. Her mane and tail will not grow. Other horses, as strange as it sounds, tend to eat it. The current owner has had this horse separated from the others for over two years now, but its mane and tail have not grown a single inch. My question, is other than the horse wouldnt do that great in dressage, will it cause any problems? Like she has no tail to swat away mosquitos, so maybe she is more prone to West Nile? Anything i should be concerned about? (other than looking a bit awkward, she is a great horse)