
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. [Colloquial; c. 1920]
An investor who isn't comfortable with investing and the risks associated with it.
Investopedia Says:
If a nervous nellie ever does decide to invest, he or she is likely to liquidate the investment at any time.