You must defeat Myzrael before she grows in strength.  If you do not, then once she has gathered enough power she will challenge her captors!  There are some who think they can control her, but if she can be controlled then why did the giants chain her in the first place??$B$BCrazy logic, eh?$B$BTo defeat her, summon her at the Shards of Myzrael where you first spoke with her.  Defeat her and gather her Eldritch Shackles, then bind them to the Shards of Myzrael.$B$BDo that, and she will again be trapped.