I kissed my cousin once, when I was 12. She was hot, we were at a family reunion in Baja. Creeped both of us out.
The idea of having a jacuzzi party with her now? Eww
So you've never hung with friends in a hot tub? So you've never hung out with family in a hot tub?
Seriously?
I've been in a hot tub with cousins, friends, friend's gf's, friend's wives, etc. It's just a hot tub, when it's big enough, usually everyone joins in.
Is it possible you were drunk, loud and just plain obnoxious when she told you to go to bed?