I have had my niece over a year.. Her mother who is an addict has disappeared for over 6 months. And is now attempting to contact her. Is the face that she has not contacted her in over 6 months considered as child abandonment?

It may be, but what do you expect that do for you? You say you "have your niece", under what legal terms do you have her? What is it, exactly that you want?

You may want to check out this sticky:
https://www.askmehelpdesk.com/family-law/child-abandonment-read-first-364259.html