"Que veut leur belle-fille ?"
Translation:What does their daughter-in-law want?
The answer would probably be in the partition symbol " - " used to indicate inversion for questions or compounding of words.
So, if "belle-fille" is a compound which means "step-daughter" then dropping the partition which compounds them would make these into 2 separate words: "belle fille" would then simply mean "beautiful daughter".
After all that, it is probably just a matter of context/application.
I hope this helps!
Duolingo used to have notes sections to explain things more clearly. Where did all of that go? Please bring them back. Pleaaaaase. Why do we say "what want their daughter-in -law" (direct French-English translation) when actually what we want to say is "what does their daughter in law want?".