Thank you, Karen and Wellington! She'll be grumpy but then again she always is. Cold blooded beastie! I'm so glad I got this advice, which was consonant with my own understanding to start with, while the sun is still up.
My 15yo Iberian tortoise buried herself yesterday, about a month earlier than typical and only two days after last eating. She ate very well that time, though her appetite had dropped off a lot in October, which isn't unusual, even though it's still very summer-like where we live in that month...