Let me assure you that Northup is no pushover. I've been involved in some of her campaigns (you see her TV ads from years past). On something like this she tries to always tread lightly as her district is not very predisposed to electing Republicans (quite the opposite, in fact). In effect, this was the only issue her opponent has come up with and she just pulled it out from under him, and at the same time the stickers and the question they raise is more in the public eye.
If you want to hear how poorly her opponent is doing at coming up with an issue, listen here:
http://northupforcongress.com/cgi-data/news_doc/files/68.shtml