Silence took over the room as Aria waited anxiously for Kai's decision. She wasn't scared of death as much as she was scared of Kai dying soon after her.
That would be her worst nightmare. Seeing her goal get shattered into pieces after years of suffering and pain wasn't something she was ready to handle even if she was dead.
It didn't matter if she had to do an Origin Vow at all as it would only prove her honesty first and foremost. What was her life worth if she died and then ended up failing everything she sacrificed her life for?
It wasn't a selfish thought but more of a desperate attempt to regain hope that she did the right thing. Even if she hurt Kai doing it, she wanted to believe that she did what was best for him.