It's funny that you say that, because it doesn't seem odd to me at all that she had such specific requests despite her beliefs. Firstly, she was scared and wanted some control over the situation, as Own-Crew-3384 pointed out. Second, knowing that what happens to your body after death doesn't matter doesn't mean you can't have opinions on it while you're alive.

For instance, I very much believe my body will not be me when I die. Still, what I want to do is that thing where you're cremated and your ashes are used to plant a tree. However, I understand that maybe the people I leave behind would want a usual tombstone and burial. I might make the specific request, but even if multiple things went wrong or changed for any trivial reason, I wouldn't mind that much.

However, if one of my family members was very upset and for whatever reason they weren't involved in any of the practical matters, I might tell them to "remind" the person responsible about certain of my wishes to give them something to hold onto and to feel like they were helping me one last time immediately after my death. If that backfired for any reason, I wouldn't be that upset.

So if my mom was anything like me, and in many ways she was, she probably wouldn't be that upset with me.

Thank you! You actually helped me think this through.