I have never heard of 'Toma' in Ukrainian cultural names. This is the first time I have seen or heard it here on Duolingo! :/
Duo should choose more common and appropriate Ukrainian names...ie: Marusia, Darka, Darusia, Olya, Yaroslava (Slavka), Volodymyra (Vlodzya), Mariyka, Olena, Hanya, Tatiana (Tania), Anastasia (Nastya), Bohdanna, Svitlana (Svita), Vika (Viktoria), etc....
So... I have a question: Could you also interpret this sentence as ''This is Tom's aunt''? Because in russian the genitive for Том would be Тома. As a native russian I was a bit confused with ''Тома'' since I never heard such a name before so I thought it was Tom's aunt, which turned out to be wrong.