Mazu has these powers because She was no longer an ordinary girl, the gods had touched her.
Explanation:
What had occupied mazu's mind initially was the act of weaving till her mind became peaceful and still. She had sat down to weave because she was worried for her fishermen brothers who were outside in the water.
Mazu was able to see her brothers after she fell into a trance and became extraordinary. She had been touched by the Gods who found her to be courageous and also a person who did not show off. She was thought to have a rarest form of courage that is balanced courage and that is why she was touched.
The reason she is able to see her brothers struggling to survive at sea and the reason she is able to guide them to the largest pieces of wood was due to the gods who touched her and made her extraordinary.
It was Babylon, The Euphrates River which was supposed to be protecting the outside of Babylon was diverted by Cyrus's army so that it would be dry enough for them to walk through to the open gates that were left open.