I do not know anything about the Nāgānanda International Institute for Buddhist Studies. But I guess it could not hurt.
You said: “There are a few women monasteries in Sri Lanka, but it seems all are Theravada.”
You sound like Theravada is bad. But Theravada is the only major sector that takes Tipitaka as the basis. It is just that most CURRENT Theravada bhikkhus do not actually follow the Tipitaka, but Buddhaghosa’s Visugghimagga. What the Waharaka Thero did was to point out that key interpretations in the Visugghimagga are not correct. There is nothing wrong with the Tipitaka.