Lil Kim had a song on her debut album where the hook is "I don't want dick tonight/Eat my pussy right". That's vulgar as hell. Nicki didn't start this wave. She just hopped on and expanded on what was done before her.
There are current women rappers whose content about sex is over the top but it's no different than TI going around calling himself "The Pussy Pumper" for the first decade plus of his career in songs. Both men and women artist in all genres have gotten progressively more vulgar in how they talk about sex.