Yes, there are Buddhist and Hindu nuns, but they probably wouldn't be called 'Mother Teresa'. I don't think there are Protestant nuns, or Islamic nuns.
A nun is typically called 'Sister Someone', unless she's the head of an order.
n.A woman who belongs to a religious order or congregation devoted to active service or meditation, typically living under vows of poverty, chastity, and obedience.
PS: I might have answered the wrong question. Of course a non-Catholic can call Mother Teresa, "Mother Teresa".
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