“Bukovinac”
Sounds Serbian to me!
Gospodi Polijoy!
I checked Geni Surnames and there were no entries. According to Acta Croatica, in the middle of the last century there were 30 households with that surname, mostly in Zagreb, but there are only 3 households in Croatia now. It says mostly Croats, rarely Serbs. It says the name is found in two other countries, one of them the US. I don't know if they would have picked up families of the name in Serbia.
Anyway definitely a Slavic surname.
Her name sounds as if it relates to this area:
https://en.wikipedia.org/wiki/Bukovina
More Ukrainian and Romanian than Serbian. But still Orthodox!