Yes, if your Mother's house has been left solely to you in her will, you may claim the property taxes that you paid even though the house has not been transferred into your name yet.
In this case, you are considered the "constructive or beneficial" owner which basically means that you accept all the responsibility of ownership of the home, derive the benefits of ownership, and treat the home as owned.
You can check out the TurboTax FAQ below for instructions on entering the property taxes: https://ttlc.intuit.com/replies/3300663
