Not that her eyes were shut or blind before, but she saw not the well before; either because it was at some distance, or because her eyes were full of tears, and her mind distracted and heedless through excessive grief and fear; or because God withheld her eyes that she might not see it without his information. Compare Numbers 22:31 Luke 24:16.
Related Commentaries of Genesis 21:19
Genesis 21:19
19 And God opened her eyes, and she saw a well of water; and she went, and filled the bottle with water, and gave the lad drink.