Should a Catholic refuse to attend a cremation?

You are going to have to make it known to the people. Tell them, look, my Church is against cremation, I love your husband or wife, but I just do not agree with this, so I cannot come. I would definitely announce it beforehand rather than simply deciding not to attend and not telling them, because that can appear insulting even when you do not mean it that way. So go to them personally, tell them, and stick up for your faith. In the case you describe, you should have gone and talked to them first; this is death, and worldly people do not understand it, so next time you will know what to do.