Regarding the daughter whose parents asked to be cremated [Ask the Rabbi #239] - isn't there a halacha (Jewish law) to not listen when your parents ask you to do a sin? That is, honoring parents does not surmount other Torah laws. So wouldn't she be obliged to not fulfill her parents' request in this case?
You are correct: A child should not obey a parent's request to transgress the Torah. If it be in her power, she should see that the cremation not be done, even if this is against her parent's will.
This reminds me of a story, that I find frightening, one which illustrates the frightening evil to which a human can sink and, at the same time, the wisdom of our Sages: Not far from Luban, Russia, there lived a Jew who was a traitor to his people; he spent his life harassing the Jewish community by slandering them to the Russian authorities at every opportunity. At the end of his life, as he lay on his death bed, he summoned the Jewish burial society. "Bury me face down," he said. Then he died.
His most odd request was brought to the great Rabbi Moshe Feinstein. Rabbi Feinstein ruled that, despite the requirement to fulfill a dead person's final wishes, he must nevertheless be buried face-up in accordance with Jewish Law.
A few days after the funeral, the Russian authorities rode into town and summoned the Jewish burial society demanding that the recently buried body be dug up. Mystified, the Jews went out to the cemetery and began digging under the watchful eye of the Russians. When the body was unearthed and became visible, the Russians said, "Enough. Bury him again." Now the Jews couldn't contain themselves: "Please explain why you wanted to dig him up?" they asked.
"This man," the Russians explained, "was our friend. He was forever loyal to us. He told us that the Jews hate him so much for being our friend that they are going to bury him face down!"