It is pone to happen in yorkie but happen in other breeds as well , I found a site with some info on this condition. I am sorry for your lost. There are diseases in all breeds of dog it just more common in some then other. I hope your mom changes her mind and get another yorkie. With everything that goes along with this breed, Icouldn't imagine my life without having one. Good luck to you.
www.newmanveterinary.com/Lymphangiectasia.html