I bought my split-level house from my mother and moved in. I rented the upstairs to a couple of tenants. They use the upstairs while my girlfriend and I use the downstairs (except for two shared spaces, the kitchen and laundry room). I'm aware that improvements made on a rental property can be tax-deductible.
Given my terrible credit, the house was sold via a contract sale instead of a traditional mortgage. Also due to my poor credit, my girlfriend financed the new appliances and bought a couple of devices for the house (Nest thermostat and smoke detector). I am reimbursing her for them.
Since the house is mine but she made the purchases for the house, can either of us claim the deductions? If yes, do I have to write off only a percentage since I only use the equipment some of the time?