ok, here's her story: she was betrothed to arthas menethil, who she loved since childhood, it caused her much emotional pain to have to kill him after he became the lich king.
garrosh hellscream after being appointed warchief of the horde sanctioned a group of blood elf mages to construct a mana bomb, with the help of the focussing iris from the eye of eternity (which was stolen while being transported from one location to another by the horde), decimated theramore killing almost all its inhabitants (if it wasn't for rhonin and his sacrifice it would have been far more devastating), it was this act which finally caused jaina to snap and caused her to go on a rampage to the gates of orgrimmar with the soul purpose to kill garrosh hellscream and raze orgrimmar to the ground, if it wasn't for a timely intervention she would have done so.
so take your pick, lost the love of her life and was forced to kill him to stop armageddon, watched her people massacred by a war hungry orc with ideas of grandeur and unable to reconcile with what was done.
garrosh hellscream after being appointed warchief of the horde sanctioned a group of blood elf mages to construct a mana bomb, with the help of the focussing iris from the eye of eternity (which was stolen while being transported from one location to another by the horde), decimated theramore killing almost all its inhabitants (if it wasn't for rhonin and his sacrifice it would have been far more devastating), it was this act which finally caused jaina to snap and caused her to go on a rampage to the gates of orgrimmar with the soul purpose to kill garrosh hellscream and raze orgrimmar to the ground, if it wasn't for a timely intervention she would have done so.
so take your pick, lost the love of her life and was forced to kill him to stop armageddon, watched her people massacred by a war hungry orc with ideas of grandeur and unable to reconcile with what was done.