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One of the players in my Kingmaker game is doing this with their PC right now. There's a magic item related to Lamashtu that lets you do that - I don't know if it's Pathfinder or 3.5 but it was definitely published by Paizo.
And without going bluh bluh epic campaign story the PC in question had their biology modified by the fey of the First World. They are now trying to figure out what to mate with first, and there are some pretty (potentially) creepy options for her.
On to your question:
I don't think it is as likely to be offensive as you may fear - you are talking about creating a villain who is female, and certainly uses the fact that's she's female in her villainy, but...
You don't seem to be exploitative.
AND
She's empowered, in a way.
Don't make her beholden to some other (male) entity or individual, don't make her only about sex, don't justify things about her just because she's female. Just make a memorable, creepy villain that your players will never forget.
And make sure that she's not the only notable female NPC, and follow your sexism checklist on other ones. Try to make your world believable, including in its gender dynamics, but don't relegate female characters to the background. Make them have their own lives, viewpoints, and agendas.
Oh I could go on...