Genealogy / Birth in Lviv in 1926: Polish or Ukrainian nationality? [29]

Hello everyone!

Just a quick question that I'm hoping someone can help me answer: my boyfriend's grandmother was born in Lviv in July 1926. Was Lviv a part of Poland or Ukraine in 1926?

If Poland, would she still be considered a Polish citizen? And by that, I mean, would she be able to claim Polish citizenship by her birth?