Ugh Kaoru is such a disgustingly manipulative person. Shizuka really should have cut her out of her life.
Well she tried to, and it didn't go so well.
Only because she didn't stick with it. I find it extraordinarily unlikely that Kaoru was actually a real danger to herself considering how much of an egoist she is. She wasn't trying to kill herself she was going on a hunger strike to guilt-trip Shizuka into continuing to put up with her awful behaviour.
Well if that's a risk you're willing to take, then you are stronger than Shizuka.