Translation:They do not like their green skirts.
Elles n'aime pas leurs juepes vertes, is the answer to the dictation and I have two issues with pronunciation with respect to plurality.
This could be a woman (elle) not liking other peoples (leurs) skirts, or other peoples (leur) skirt. And it could have been A group of women (elles) not liking other peoples skirts, or other peoples skirt. And it could have been a group of women not liking their skirts or their skirt.
Just because its says, leur, doesn't mean its, Elles, or jupes, just because it is more likely, correct? Duolingo is famous for giving sentences that don't make sense. So by hearing along how do you know which is it?
If by listening to the French sentence you interpreted "leur jupe verte" and translated in "their green skirt", it would just mean that one skirt belongs to several women. In French, there is no difference in pronunciation between singular and plural: "leur jupe verte" vs "leurs jupes vertes".