Most reporting on the Bill Clinton/Monica Lewinsky scandal suggests that Hillary was in the dark — perhaps willfully — about what her husband had actually done. It wasn't until Aug. 14, 1998, that Clinton admitted the Lewinsky affair to his wife. ("I was trying to protect you and Chelsea," he said, explaining his lies.)
More to the point, the Lewinsky scandal was fantastic for Hillary (apart from, you know, that stuff that happened). You can see in the Gallup poll's comprehensive chart that opinions of the first lady surged through 1998 and peaked after Bill Clinton was impeached.
A voter born after might not even remember the scandal happening. The voters who do remember, generally, sided with Hillary, turned against Bill (personally — his approval ratings stayed high, thanks to the bubble economy and the GOP's overrreach), and rejected impeachment.
Ironically, Hillary Clinton has rarely recovered the high favorables of the Lewinsky period, but Bill's recovered completely. That's only natural, as people always look more kindly on their presidents in retrospect.
David Weigel, Slate