No, Mary never regained her sight. Mary became blind at the age of 14 as a result of falling ill with scarlet fever - her blindness was lifelong.
However,contrary to the tv series, in real-life Mary never married nor ran a school for the blind. She died a spinster at the age of 63 in 1928.
She nevers gets her sight back, But in a later season after she marries Adam, She has the ability to see warmth and they think she is gunna get her sight back but its just her eyes seeing warmth and light. Later in the show Adam gets hit in the head and regains his sight and becomes a lawyer.