Question about damage liability in a homeowners claim

Hi all,

Maryland resident here. A claim was filed for water damage/sewage about a month ago on a family members home. The homeowners insurance company sent out a mitigation team (different company) that ultimately dropped the ball and caused more damage. To make a long story short, this company allowed for sewage to sit underneath the property (dirt crawl space) for over two weeks, while running dehumidifiers and fans over it. The sewage was not cleaned in a timely manner and this stalled the process significantly causing more damage including rodent infestation. The insurance company is saying that she must go after the mitigation company and they are not responsible. Is this true? How would you proceed in this matter?