Nobody should ask DIL to spit up her husband's remains or send them to her mil. Whether your grandmother gets an all expense paid trip to the memorial service on your mother's dime is a relationship issue not an etiquette issue. Either way is perfectly polite. I'd stay out of it if I were you, and if your mom pushes just tell her whatever you believe. For example, "Mom, you have to learn to stand up to Granny. Telling her 'no' is the only reasonable option given your financial situation." Or "Mom, you can afford to send Granny to the memorial service, and it isn't worth the fight with her for your own mental health. Just plan it and get it over with."