Taida na Akujoku Kizoku ni Tensei Shita Ore, Scenario o Bukkowa Shitara Kikaku-gai no Maryoku de Saikyou ni Natta - Vol. 1 Ch. 2

[Carn109]

Lilith is packing heat
That killing aura must be something else

 

[maylsmallow]

I like Lilith!!! She's cool

 

[hevensdragon]

so I think the real question is, why was someone of her caliber allowing herself to be abused by the original Weiss. Guess we'll find out in later chapters

I mean, real answer. Many case of assassins are put through hellish training since young and trained not only to be strong but blindly obedient. His abuse may be normal to her, it could also be light compared to what she was raised with so she sees it as kindness.
Lighter note, she could enjoy it, you just never know.