Death scared Hazel. Of course, almost everyone feared death, even subconsciously. But for her, it was different. She wasn't afraid of it because of her time spent in the Underworld, or even the cave in all those centuries ago. Hazel Levesque feared death because of what it did to the ones left behind.
Nico's sister had been killed years previously, but he was still an emotional wreck. He spent his time alone, refusing to talk about his feelings. Instead wallowing in his own self pity, constantly wondering why he even bothered continuing on the with the hell otherwise known as life.
Leo had killed his own mother, and Hazel often heard him crying himself to sleep, and screaming once the darkness finally overtook him. He used jokes to hide this misery, but Hazel knew the truth.
But when Hazel miscarried weeks before her twenty fifth birthday, with Frank worlds away on deployment, she felt the after effects of death like never before.