And since when is Krieger repulsive?

While Amy is an actual physicist, it’s unclear whether Cheryl is an idiot or insane. I mean, she’s certainly insane, but that can make say and do things that come off as incredibly  stupid. At times, though, she appears to be quite intelligent and well-educated.

She's probably just insane since she has occasional moments of clarity and intellect.

You could also argue general sluttyness for both.

Both of them are (at least early in the series) promiscuous.

She's still a ditz, even if she's supposedly a genius which always seemed out of character to me.