When you think about it, Nicki really did reinvent the whole archetype of a "Female rapper".
Before her, most rap girls didn't feel the need to sing or add pop into their sound. Since Nicki made it huge though by being versatile, who have girls like Iggy, Bankrupt, even Kreayshawn and others following the same path of blending their sounds with pop and singing. Most upcoming female rappers would probably do the same if they were trying to make it.
The one thing they have failed to replicate, however, is Nicki's business savvy and knack for strategy. Hence, Iggy and Azalea, the two biggest female rappers after Nicki, can't even their debut albums released and still haven't really found an audience in America.
The thing they failed to replicate is Nicki's extremely catchy and memorable verses.