Desperate Housewives!! really confused!!?

In desperate housewives, when the black lady who could play the piano put the poison in her son's ice cream, i thought he was dead. and when she returned to her house, mathew, her other son, said, "is it done?" and she said "yes, we can mourn for your brother later." BUT then.....in the last episode of season two, i saw the lady get into the car with the son she had poisoned (i think his name is kaleb.) so i'm REALLY confsued!!!!! someone please clear this up for me!! thanks!