What is a theft gain for this case, and what is the basis of the coin collection Sofia received?

One month before she died on April 14, 2011, Maria Chavez (Sofias mother) gave Sofia a coin collection. Based on careful records that Maria kept, the collection had a cost basis of $9,000 and a fair market value of $18,000 at the time Maria passed away. On February 12, 2021, the Arroyo residence was burglarized, and the coin collection was stolen. The Arroyos filed a claim with the carrier of their homeowners insurance policy for $24,000 (the current value of the collection). Unfortunately, they were only able to collect $10,000, which was the maximum payout allowed for valuables (e.g., jewelry, antiques) without a special rider attached to the insurance policy.