I researched this and Lucy actually does mean what I say it does in the story.
"Ooh, Benjamin, it's beautiful."
Lucy's smile was like a thousand rays of sunlight. Benjamin Barker had been flushed and embarrassed that she'd been so pleased with his gift.
It was a necklace, and something he had researched thoroughly. He had wanted to give her a gift with meaning—the word "Lucy", he had discovered, meant "light", and so he had it set in his mind that he would give her a present that exemplified her name. Plus, she was his light. It was a fitting idea for gift.
The necklace was lovely. He had bought it from a street vendor at the market. It was silver, fine silver, with a bauble at the end in the shape of a ball of light. He had known from the moment he saw it that it was the perfect gift.
And then, as he saw her gaze at it in wonder with a hugely pregnant belly and a smile that warmed his very soul, he knew he had been right.
The perfect gift for the perfect wife and the soon-to-be perfect mother.
"Put it on for me?" She'd asked sweetly. He'd obliged with pleasure. He'd opened the clasp at the back and watched as the silver slid down her slender neck. She'd looked at herself in their large mirror.
"It looks lovely. I'll never take it off," she'd said.
"Mr. T?" Mrs. Lovett asked, interrupting his thoughts.
Sweeney Todd looked at her as though noticing she was there for the first time. He had been completely immersed in his thoughts.
"I'll never take it off."
At the time, he had taken her words to heart. But now…he knew somehow that Mrs. Lovett was telling the truth about the necklace. But if she was telling him the truth, then why had the necklace been in a heap on the floor in the corner? Had Lucy cast it aside after he had been taken away? Had she never really liked it after all?
"Mr. T?"
He found Mrs. Lovett irritating most of the time, but right now she was really irritating him.
"Leave," he said quietly.
"But—"
"LEAVE!" He yelled at her. When he looked at her, he saw a thousand kinds of hurt in her eyes. But she left.
He was left to wallow in his own despair, clutching the necklace and wondering about Lucy.