I don't know if anyone remembers that, but Dahlia was an extremely strong character to have such a weak death.
she was abused for years or decades by the vikings and yet she remained standing and strong. she helped her sister even after Esther chose to stay with the man who abused them. she had her life lost because of these abuses, as she was always branded as one of the most powerful witches in history and refrained from doing anything against Mikael because of the love that Esther had for him.
years later, tired of having this, she seeks revenge without being very noticeable. Freya says that the only way to kill Dahlia is with the ashes of a Viking, so Niklaus finds a way to kill Mikael, so Dahlia has her first revenge.
then, she destroys the indestructible white oak in an attempt to wipe out the people she "gave life to": the originals.
in short, Dahlia was one of the few most notable characters in this universe, but they were no good at developing or keeping her alive to fix many things.
Esther and she could live in a remote city and Dahlia could take Inadu's power for her, after that, they wouldn't have to kill the boys.