Are you getting her as a pet? They should have had her checked by the vet a long time ago. I would be concerned about a breeder who has allowed her to bleed for 2 months and not had her checked out! I can only assune they did not have her checked, or they would know why she was still bleeding and have been able to tell you.
Could be an infection or many other things. She likely will need spayed.
I would have her examined at once by a vet. Not only is it abnormal for the dog to be bleeding for that long after a heat cycle, she should be spayed a long time ago. There are so many conditions she could have, but one thing she will have is a lack of iron, leading to anemia. Let us know how she is.
Could be pyometria. Since she's six, it could also be a sign that she is developing or has developed a polyp (resulting in a need for tumer romoval along with the spay). All kinds of problems start to show up around that age in an unspayed female having to do with the fact that she has not been spayed. Definantly past time to get her checked out and get her fixed I think.