The first stanza speaks as if it is a mirror. The second speaks as if it is the water of a lake. Both speak about their power of reflection which means they tell the truth, report exactness, and the repetition of what they see. The mirror reports what appears to be fact, whereas the lake seems to have relationship and power to change the woman.
The big difference between the two then, is the depth to which a person may engage with the reflection. The lake provides the ability to die and to resurface differently. At the lake, a woman engages:
"A woman bends over me, searching my reaches for what she really is"
This demonstrates a much more intimate relationship with the lake. Further on, the lake reports:
"She rewards me with tears and an agitation of hands.
I am important to her. She comes and goes.
Each morning it is her face that replaces the darkness."
The lake longs for the company of the woman and senses the woman's pain. The mirror seems incapable of this.