"The holy grail has gone missing!"

Cause this! She do not give two ducks about what be going on in that household

Pretty sure its the dad who hid it
Then gonna spout bs that they need to do the ceremony with the cup for her to be realized as the new head

Tradition for centuries… she need to use that during the official ceremonies where all the nobles will be attending including the head of the main houses.
It’s the ceremonies to officially announcing that she has became the head.
If she don’t have that, some family may purposely cause rumours or whatever that could threaten MC’s position…
Well, treat the holy grail as a very useful politic item the MC need.