Is there a time limit for an estate heir to respond to the opersonal representative or the courts?

We won a court contest litigation case in July 2010. By Michigan law, the estate is to be divided between the heirs. In this case that means 50/50 between my hubby and his sister. However, we can not get his sister to respond to us and all mail has been returned saying that it is undeliverable. Because of this, we are sitting ducks on the distribution process of this estate. Is there a time limit for her to respond to us or the courts?|||yes, there is