For starters, you ask for a feminine equivalent in your question, but the original phrase does not necessarily (and in the case of pirates, is unlikely to) refer to same-sex-encounters.
Now, the word priapic originates from the name of a minor Greek god, who was know for his, let's say, outspokenly present and continuously active masculinity.
One option would be to find a female equivalent, and the one that comes to mind is Aphrodite or Venus.
The adjective for Venus is venereal, but I doubt venereal conquests would have any positive ring to it, because of the common association with venereal diseases. You could try aphroditic conquests, maybe.
Alternatively, you could look for something more physical, as priapic is a direct hint at the erect penis. Although some parts of a female body may become erect, I am not sure that those erections evoke the same image or impact as the priapic one.
However, you could throw in (an allusion to) some other parts of the female anatomy.
Labial conquest comes to mind, but it might mean that they relatively innocently kissed someone.
Vulvic conquests would be an option I guess, descriptive of the kind of conquest.
You could play around with adjectives based on less formal nouns for the female anatomy, but I will leave that up to your own imagination and what you see fit for the context.