In me she has drowned a young girl (17)
This quote reveals part of why the woman is so disturbed by her reflection – she has seen her own youth disappear. Her loss of youth takes on a connotation of devastation by the use of the word "drowned."
In me an old woman Rises toward her day after day, like a terrible fish. (17-18)
This quote reveals the second half of why the woman is disturbed by her reflection. Now that the young girl is gone, the image of the old woman she is to become rises up at her, rushing at her as if it is going to swallow her into the waters. The last phrase in this quote, "like a terrible fish," shows the horror and disgust that this woman finds in the coming of old age.