Idk, I feel like Anastasia could’ve very well know what was the tomb for exactly, especially with her planning such a long game

if she indeed was closer to Alecto even before her failed ascension, she probably would not be up to other OG lyctors intent of getting rid of her and would oppose that

so John is like ‘they are forcing my hand and RB is a real threat, but you know I love her so much and never would be able to kill her(more like can’t), so why we won’t just put her to sleep with you watching over her till she wakes up, set up traps and wards against other lyctors but they also can never know she’s not really dead so we gotta do a little sewn tongue’

don’t know if John would tell about the rock and blood ward right away tho

and between tomb building and Alecto’s entombing, Anastasia could’ve figure out something more or initially mistrusted John, so she hatched her own little scheme