Our daughter was 27 mos when she came home, we kept her Ukrainian name, Anastasia, but she was called "Nastya" or for a nick name in UA. So we began calling her Anastasia Nastya the first couple days, as time went on we dropped the Nastya (about a month or two) she had no problems answering to Anastasia.
Fast forward a year and a half later... at the age of 3 1/2 she was in preschool we were talking about our names (I was her teacher) and when she was asked what her name is she answered "Nastya" so we have really worked on her name since then. Asking her what her name is very often for the coming months, she now answers "Anastasia". But she does tell you "In Ukraine they called me Nastya"
If she is very intently doing something and doesn't answer to Anastasia, she will answer to Nastya!! Interesting.