I was told by a writer that when writing a Narrative Essay the opening sentence should be vague and ambiguous. Is this a true statement?

My narrative essay is about fracking but it is told through the eyes of an environmentalist lawyer who speaks with a frantic 10-year-old girl concerned about her friend's life. They had been playing in a pond and not soon after her friend is hospitalised. Therefore she suspects it had something to do with the pond. The lawyer will put two and two together as she tells him the story. It will be like banter, her telling him aspects and then him asking questions to dive deeper into the details, therefore gathering sensory information about the scenes.

Anyways, here is my opening paragraph. Tell me what you think of the opening sentence, should be changed or scrapped completely? Please give your critique of the rest as well. Thank you

The day I met Sarah is one I will never forget. Working as an environmentalist lawyer for a small firm in Pennsylvania, I come across a lot of cases; Sarah’s was one that moved me more than any other. I remember when I met her; it was about a year ago to this day. The misty morning dew was ever-present, and vapors filled the air of the street corner overlooking my office trailer. Sipping a cup of decaf and reviewing a few old papers I glanced out the window to a see girl no more than 12 years old. She was vigorously zigzagging her pink bicycle throughout the fog. I could tell she was distressed by the frantic look on her face. As she got closer she eventually tossed her bike to the ground, slightly bending one of her bike mirrors. Her footsteps were quick and direct as her shoes sloshed through the mud from the rainstorm the night before. As she gradually walked up the stairs of my office, I contemplated what she might say. Her fist pounded on my door “BANG! BANG! BANG!”. “Come in” I said. As the door slowly crept open, a sad and gloomy face appeared before me. In an uneasy and shaky tone she said “Mr. Dreicer, please help….my friend’s life and many others are in danger if you do not help.” What she began to describe to me would change my life forever.