A timid or cautious person; a worrier: a nervous Nellie a bit like Jeanne Dixon
[late 1930s+; perhaps fr Nervous Nellie, the nickname of Frank B Kellogg, secretary of state 1925–29, who negotiated the Kellogg-Briand differences]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with nervous Nellie
An unduly timid or anxious person, as in He's a real nervous Nellie, calling the doctor about every little symptom. This term does not allude to a particular person named Nellie; rather, the name was probably chosen for the sake of alliteration.
[ ; c. 1920