My question involves landlord-tenant law in the State of: Virginia

Have tenant in SFH with 3 year lease ending July. 16 Nov tenant emailed about our return to house in July. On 18 Nov. she emailed that she may move earlier. Same evening she contacted property manager with heating issue. Contractor was called and 21 Nov diagnosed and ordered parts. On 22 Nov tenant reported empty propane tank (filled 300 g on 11 Oct). leak test performed that day with no leak found. Tenant says we (landlords) should pay as it was related to heating issue. Tenant was gone for a week for the holiday so repair delayed until 4 Dec. When repair was made to the furnace - repairman found that due to faulty wiring the propane furnace was acting as primary heat rather than aux to the heat pump. Again tenant says landlord is responsible for the extra gas usage. As landlords we acted to fix the problem as soon as it was identified. Tenant claimed that the heat was not working or running constantly since the beginning of Nov, but she only notified us on 18 Nov. Tank was filled Oct 11 & ran out by 22 Nov (4 days after we were notified of problem), I suspect that the problem was of longer duration. She states that she will move and end lease asap.

Are we liable for the extra propane usage? Can she use this issue to move out early? Should we pay something towards the cost of the gas?