Can a woman be an Acharya?

Yes. Women have shown the spiritual path to others from Vedic times. The Brihadaranyaka Upanishad tells us of Maitreyi and Gargi who were the wives of Sage Yajnavalkya.

They expertly conveyed spiritual wisdom to their students. There were other scholarly women too in the Vedic times and are known as Rishikas. Their poems are part of our Vedic heritage. Sri Ramanuja himself directed his students who had doubts about the Darsana to go to the lady, Kongu Piratti, and get the right answers.