When something like this happens, it has always worked for me to delete the entire entry for that person and then add them again. A social security number can begin with a zero. That should not be a problem. What happens sometimes with any computer program is that there is some hidden character that is causing the field to be misread.
Programmers used to call them gremlins. No matter how correct the field looks, it is being misread and giving a very frustrating error. If deleting and then adding her information back does not work, contact TurboTax help desk to have an investigation opened.
I am sorry that this happened and assure you that any "bug" will be addressed.
