Lily highly doubted that there had been eighteen years without an opportunity to do something, even anonymously. And Severus was clever, he would have found a way to contact her if he really wanted to.
"I can't, Severus," she said quietly. "I just can't." She was about to 'I'm sorry', but stopped herself just in time. "If you're not going to kidnap me you can let me go now," she said, instead.