My real-life grandmother made from-scratch vanilla extract this past summer. I learned it is made with vodka, which is also how I learned why it is I love vanilla extract so much.
Please don’t use cedar ashes in your cookies, folks.
This scene has gone through so many iterations it's insane. In the cruelest version, a version which probably borders on character-breaking in it's awfulness, Mari wrapped up the urn as a gift, with paper and bow and everything, and gave it to Andi during the gift exchange in front of everyone. Interestingly, every discarded variation has a common reason for not being used: I just can't see a feasible scenario where Mari would give Andi the urn or have this conversation in front of the girls.
Grandma Mari knows darn well Selkie is not inclined to take a bite of any type of cake, rum-infused or otherwise. But dialogue wise it felt more "grandma-y" to me for her to express concern over both kids accidentally imbibing liquor, instead of singling one out over the other.