Dunja

In Serbia and several other countries the name is indeed derived from the name of the fruit (quince). It's common in these cultures to name girls after fruits. Jagoda and Visnja are common names and sometimes Malina is also being used. So in these countries it does derive from the fruit and is spelled Dunja.

---

Dunya is a completely unrelated Russian name that has nothing to do with Dunja or its etymology. I doubt that many people in Serbia etc. had the Russian name in mind when they gave it to their daughters as Russian names aren't currently very popular thanks to the history and complicated relationship with Russia. There are still some names of Russian origin in use but they are declining in popularity. As Dunja is still quite popular I do believe it is generally given with the fruit and that etymology in mind and not with the thought of the Russian name Dunya.

---

Dounia is yet another variant that means 'life' or 'world' in Arabic and is common in many countries in which the language is spoken.

---

So you have three very different names that all sound the same but are unrelated.

While Dunja may refer to quince, and as such is used as a reference to a women in songs, Dunja is also a given name that comes from Russian Avdotya. Russian nicknames are most commonly used as first names in Croatia and Serbia. [noted -ed]

This is not a variant of Dunya but rather it derives from the word for 'quince'. Serbs have a tradition of naming girls after fruits - Jagoda (strawberry), Višnja (cherry), Jabuka (apple) etc. Therefore Dunja (quince). [noted -ed]