So the Horde players hated her as they feared she will take the place of Sylvanas, that is not the case.
Calia was never treated with respect, as her Kingdom had some interesting rules. A woman cannot be Queen even if she is the oldest, so the crown would go to Arthas giving him all the attention.
Calia is merely a princess at that point. She was almost married off to Deathwing, by an arranged marriage and no one listened to her cries.
She later married in Secret to a man from Southshore, where she had a daughter with him.
When Arthas Attacked and killed her father (and possibly her mother) she ran away fearing for the worst. Undeads everywhere, people screaming, She hid in a muddy ditch for 2 days until she reached safety. Now imagine what that was like? Soldiers these days are trained to hide in a muddy ditch for days without food, Calia… she wasnt trained she is just a Princess.
She managed to reach Southshore and stayed there hiding until the Cataclysm where Undead (her own people) attacked the city and gassed it. She lost her Husband and Daughter not knowing where they are or if they are alive. She screamed and cried.
In Legion it appears she became a Priest.
In BFA she was killed by Sylvanas Windrunner while protecting her own people (both Humans and Undead of Lordaeron) sadly, she along with the Undead citizens were all killed.
She was raised by the Light. Not fitting in on the alliance, or the Horde. Not exactly human or undead.
The Horde dont fully accept her, and neither does the alliance (Tyrande was very mean to her)
She doesnt want anything to do with the crown, she just wants to see her people (both human and undead) prosper.
Worst part is, she never got to see her home. It was gassed during the war.
when looking for a tragic story, Calia is it. not Arthas, not Sylvanas.