Hi,
I'm writing a series of novels that encompass a whole slew of different mythologies and need a correct Gaelic translation for a character.
She's a paladin that has a reputation for being called the "Pale Death" amongst monsters. I know there is Bás Bán but I'm not sure if there is a feminine version of this or not as Báis Bháin has also been suggested.
Thanks in advance!

I assume that you're asking for Scottish Gaelic, and not Irish. Bás Bán would be the Irish form (see more info below).
The word bàs does not have separate masculine and feminine versions (in either language). It's grammatically masculine, so the following word remains unchanged as bàn. Note that, in Gaelic, the accent in each word slants in the opposite direction from the way it does in Irish. I've enlarged the words so that you can see that better.

"Báis Bháin" makes no sense grammatically in Gaelic (or Irish).

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

Thanks for that! I was just a little concerned that it may have been different but that helps a lot. Thanks again!