According to Wiktionary it's aurten.

With औरत you don't pronounce the 'a' in त, but with औरतें you have an /e/ instead of the 'a' so you have to remove the previous 'a' in र.

Right, I have the same question

/aurateṅ/ Can you be more specific about the question you have? It's /e/ with nasalization added.

They're synonyms. They both mean the same thing. Duolingo is just teaching you "aurten" first

Mahila is more formal than aurat.