pls helpppp

ok so im looking for this manhwa but i forgot its name….
basically the fl reincarnates into the body of a villainess with red hair, but the twist is that she is pretty weak. its kind of like an hp points thing, like for example when she gets stressed she gets negative hp. and so she marries a white haired duke who the previous lady was in love with…
oh and she also has a brother who’s a pretty powerful mage and he figures out that the person is not his sister
AND ALSO her health was compared to some sort of fish thats really delicate if im not wrong, pufferfish or smthng if im not tripping?