I'm not up-to-date on current etiquette but what my elderly mom has always done is get to the memorial a few hours early and help cook and prepare, and if the meal is catered, she still gets there early and helps set the table(s) and make certain the host feels comfortable in her difficult time; losing a mom is indeed difficult. Write the close family members (other children of the deceased, husband, known siblings of the deceased) a short heartfelt letters, and help them grieve and mourn. Insofar as sending a card: DON'T. Cards are too impersonal; send a short letter, instead. Don't know what to say? Go to a postcard shop and read sympathy cards to help guide you but do not copy poems or exact words from cards (what if someone sends a card with the same words? Awkward, yes?) Good luck and best wishes on such a sad day for many friends, family and relatives of the family.