What type of lawyer do I contact about slander ?

My xhusbands sister called a foster/adoption agency that had placed an infant with us. She said we had abuse going on in the home, alcoholism and financial instability. All were untrue but the agency had to remove the infant to protect the best interest of the child. The agency will no longer work with us. I have been divorced for 15 years and have not seen this x-sister in law except at the graduation of my high school children 2 years ago. She is upset over financial matters going on in the family and made this call to screw me over. Is this a good case for slander. and what type of attorney should I be looking for?