The Maid let someone other than the master of the place make drastic changes to its exterior and interior. That kinda stuff should not have been approved unless her actual mistress was there. The maid should have refused any proposed refurbishments in her masters stead, so she pretty definitively failed to represent her mistresses will as she should have. I'd say she deserved it. (well maybe not the targeted avalanche xd)
Also to add, even IF Prince Moron was there (and you KNOW he was there) to ENFORCE Sister's will! Nothing was stopping the Maid from REVERSING the changes AFTER they left, she kept them LIKELY thinking her Mistress would be "happy her little sister is SO considerate of her!" stepping on a LAND MINE ignorantly! Most HATE FMC for acting up on the maid like this and some calling her REAL EVIL despite the story STARTING with her being SAVED from assassins send to KILL HER by her evil Ex!
It would be funny if the sister REALLY isn't evil, just a sheltered Fool who doesn't FULL realize her actions and the fact OTHERS have made it NEAR IMPOSSIBLE for any good deed her way for her sister to EVER have worked out in her favor cause to FMC she has to see ANY AND ALL ACTIONS as having MEANING behind them, she WAS being trained to be a QUEEN after all! In politics, even "Small" things that don't look much, could mean ALOT with more context! Sister REALLY likely thinks FMC did everything for HER SAKE and NOT that EX's wanted a "weak naive woman to feel like a BIG MAN in protecting" and her parents are SPOILING ENABLERS who likely ONLY okay the exile and change over because they are SURE the Crown Prince got the OKAY from his parents to do so who I have to wonder if they ARE aware of what he did! Guessing cause he had NO REASON to send assassins, and their BEST ones after her for no good reason other then "he didn't like her" unless he was hoping "when she suffers an ACCIDENT his parents would have no CHOICE but to OKAY his action to switch her out, while ALIVE his parents will throw the HAMMER at him and he'll be forced to COMPLY and bring her back along with SETTING SISTER ASIDE! A HUGE ego hit to his groin area at how SMALL he actually is! As if this is ONE GIANT EGO TRIP OF HIS! Yeah no wonder if his parents wanted FMC to be Queen to keep HIM in check and like many before him. Took advantage of them be Pre-disposed to act out his actions! It's the only thing that makes SENSE for wanting FMC dead! And make him a PRICK too that he can't JUST disgrace her by taking her hard work and sending her to GOD'S ARSSEHOLE, he has to kill her to in order to get his way....well we have KING HENRY TUDOR as one of MANY examples of MEN WITH POWER IN HISTORY WHO KILLED THEIR WOMEN WHEN THEY WANTED A NEW MODEL! Yes he killed two, but you know he'd have killed the others if there weren't CONSEQUENCES for doing so! There's also the possibility he KNEW she was competent and FEARED someone else PICKING her up, creating a DANGEROUS enemy that had JUSTIFIED reason for revenge against him. but knew if he tried to execute her, it would look bad for him and ESPECIALLY the "Replacement" so tried to have it SILENTLY done before anyone noticed. Now he'll likely KEEP bothering her becuase he won't be able to REST EASILY knowing she's out there likely PLOTTING AGAINST HIM, reminder this is an EGOTISTICAL asshole, so OF COURSE the world revolves around him