When should I start a new paragraph or line? I have a story with a lot of dialogue.?

This story is for my narrative writing exam. It includes a lot of dialogue, so I'm confused on where I should start my new paragraphs, or where a new line suffices? I know you should have a new line for a new person speaking, which I have done. But where do I put my paragraphs? In random places in the story?

This is the first part of my story. Where should I insert paragraphs? I need this to be perfect for my exam.

I knew it was the last time I would see her.

Tears stained the girl’s porcelain skin, leaking from her red-rimmed eyes and glistening on her thick dark eyelashes like frost on a spider’s web. Thick hair, as black as charcoal, cascaded down her exposed shoulders; a flimsy inky dress hung loosely from her shoulder blade. Her frailness reminded me of a china doll, yet she shook like a leaf, her eyes big and frightened like a cat drenched in ice cold water. Her bare feet teetered dangerously on the metal rail; one gust of wind would be enough to send her off balance.

Despite the worry and tension bubbling in the pit of my stomach, I began to speak in a calm voice. “Just stay there, girl-”

“Marabelle,” she interjected harshly. A beautiful name, I thought, fitting of her beauty, yet so contradictory of her unpleasant situation.

“Marabelle,” I corrected myself swiftly, carefully edging my foot closer towards the railing. The action was not unnoticed by the young girl, whose dark eyes snapped towards it, effectively freezing the body part in place. My hands went in to the air instinctively, palms facing out, a gesture that I hoped would convey my peaceful intentions. “I don’t mean to hurt you, Marabelle-”

“They all say it,” she cut across me again. Pain and anger were ablaze in her dilated pupils as she stared directly into mine. “None of them mean it.”

I took five seconds to compose myself, exhaling and inhaling slowly. Let the patient have time to think, as well as you, my manager had always reminded me. “They don’t mean what, Marabelle?” Another trick of the trade: there was no such thing as overusing a name. “Who doesn’t-” I didn’t get far before I was interrupted again. She seemed to enjoy doing that.

“Everyone.”