Trasha is definitely not a good mother. She has abandoned her first child completely, even later when she has the chance and the power will continue to pretend that he doesn't exist (of course, a couple of times in the novel they describe her as sad about the separation... but three tears don't make a good mother, if for the rest of the time you think only of yourself); the second child is even thrown on the floor in a moment of madness, and she won't be allowed to approach her anymore because they fear that she might hurt the baby (Viscountess Verdi will take care of it).
Even in the only one thing that could redeem her, motherhood, Trasha fails miserably...