Marés da Guerra. Está dito claramente lá, em mais de uma ocasião.
Não vou procurar a obra toda por tais citações. Basta dar uma lida na wowpedia:
After the fall of Theramore to Garrosh's mana bomb, Jaina became deeply affected by the trauma of the event. For a time she believed that her father had been right, snapping out of it only when Kalecgos compared what she was doing to the culling of Stratholme. Though still strong and independent, she is no longer as friendly or as trusting as she once was, especially to the Horde. Jaina has become committed to removing Garrosh from power. Though the initial rage she showed was a side-effect of the bomb, she is much less tolerant of orcs now (though she no longer possesses the desire to kill them all, and realizes that not all of them are like Garrosh) and has ceased her friendship with Thrall, citing him as the root cause of Theramore's destruction as he placed Garrosh in power in the first place. In spite of this, she admitted that peace may be possible if Garrosh is removed, and admitted that she wished she had parted with Thrall on better terms, implying that it may be possible to mend fences later on. She also felt guilt for planning to wipe out Orgrimmar. Even so, she is more bellicose now and will not hesitate to act militantly to those who threaten the security of her people (although she draws the line at killing non combatants).
No Epílogo de Marés da Guerra, quando o Kirin Tor pede que ela os lidere, o próprio Aethas Fendessol diz que a sua ira pode ter sido causada pelo efeito da bomba e a encoraja a assumir a liderança. (sim, nesse caso Aethas deixa na dúvida, mas o livro mostra o efeito adverso como certo).
Editado: Todos aqueles que estão perplexos com certas atitudes de Jaina: leiam o livro (*). Vai esclarecer muitas coisas e mostrar que ela, apesar de estar agindo mais militarmente agora, não é um algoz, mas sim uma vítima.