re: Recourse against Garcia Roofing

Flashing is a common leak point if its not done correctly. Garcia would have/should have done the flashing when they installed the roof, so its definitely their fault. If the roofing company is being uncooperative, try posting on their social media, threaten lawyering up, going to the news, better business bureau, etc
Another option is filling a claim through her homeowners insurance. They would cover the cost of the interior repairs (but not the flashing repairs) and probably subrogate the roofing company for the costs and her deductible reimbursement. If immediate repairs to the flashing and/or interior are necessary, take extensive photos of the flashing issues and all damages, and save all receipts.