Christmas Present for awful SIL

[BanKittenHeels]

I hate my SIL, she hates me. I haven’t seen her in years, she has treated me appallingly in the past.
She will be at our family Christmas for the first time in 20 years, we have to get her Christmas present because she is the queen of petty and will get me one just go be seen go do so.

What the hell do you buy for someone you hate and have no clue as to their personal tastes?

Skipping getting her a present is not an option.

I would get two gifts.

One that I would like myself and would stash somewhere and another evil 'horrible cow' gift.
If she turns out to have had a personality transplant then she gets "good" present. If not, I get to keep good present and give her "horrible cow" gift

Not your job. Let your DH sort out a gift for his sister.