They didn't make her a slut.
She`s pretty badass; plus, way more independant. Instead of being a sort of Robin to the Joker's Batman; she`s an independant, stand-alone character who can produce her own storyline.
The DC reboot is actually really good; don't diss just because you dislike the fact that they modernized Harley's design. Because, let's face it, her old one was outdated.