Hello Bjnorvell, welcome. A mermaid represents a merge between your conscious (human half) and unconscious (animal half) self/aspects. Perhaps she is dead because there has been a recent failure to recognize, acknowledge, or attend to (didn't see face) the emergence of unconscious aspects of self.
I'm not quite sure how to relate this to your waking life.
Have you been ignoring something within yourself?
Has a previously unknown aspect of yourself recently emerged which you have denied or failed to recognize/acknowledge?